JP2009003456A - Imaging device and exposure controlling method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging device and an exposure controlling method for determining an exposing value based on a luminance level. <P>SOLUTION: This imaging device for controlling the exposing comprises an imaging unit for imaging an image of a subject, a photometric sensor 54 for measuring the luminance of each region of the image, an abnormal luminance region detecting section 210 for detecting, from the image, an abnormal luminance region where the luminance is locally high, and an adding circuit for adding the luminance of a region other than the abnormal luminance region detected in a surrounding part of the image and calculating the exposing value when the image is photographed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an imaging apparatus and an exposure control method. In particular, the present invention relates to an imaging apparatus and an exposure control method that determine an exposure value based on a luminance level.

  Conventionally, a method for determining an exposure value based on an average value of luminance of an image is known. Japanese Examined Patent Publication No. 8-7361 discloses an automatic exposure adjustment device that increases the priority of the main area in the center of the image and controls the exposure so that the main subject is in an optimal exposure state.

  However, when the exposure value is determined based on the average value, if there is an abnormal luminance area with extremely high local brightness, such as a light source, in the image, the overall luminance average becomes high, so that the exposure is suppressed. Therefore, exposure is suppressed in areas other than the abnormal luminance area, and the main subject is underexposed. Also, if the priority at the center of the image is set high, the abnormal luminance region existing at the center of the image cannot be excluded. As described above, the presence of the abnormal luminance region has hindered obtaining a good exposure value.

  SUMMARY An advantage of some aspects of the invention is that it provides an imaging apparatus and an exposure control method that can solve the above-described problems. This object is achieved by a combination of features described in the independent claims. The dependent claims define further advantageous specific examples of the present invention.

  That is, according to the first embodiment of the present invention, an imaging device that controls exposure, an imaging unit that captures an image of a subject, a photometric unit that measures luminance for each region of the image, and a local area from the image. An abnormal luminance region detecting unit for detecting an abnormal luminance region having a high luminance in general, and an addition for calculating an exposure value when the image is photographed by adding the luminance for each region of the image excluding the abnormal luminance region Circuit.

  The abnormal luminance region detection unit may include an abnormal luminance region candidate detection unit that detects a region having a predetermined luminance or higher in the image as an abnormal luminance region candidate.

  The abnormal luminance region detection unit may further include an abnormal luminance region selection unit that selects the abnormal luminance region candidate as the abnormal luminance region when the area of the abnormal luminance region candidate is a predetermined area or less.

  An absolute reference value storage unit that holds in advance an absolute reference value that is regarded as abnormal luminance, and a luminance average of the entire image is calculated from the luminance measured by the photometry unit, and a relative luminance that is a predetermined value larger than the luminance average is obtained. And a calculation unit that determines the predetermined luminance based on the absolute reference value and the relative luminance.

  The abnormal luminance region detection unit may detect a region including a light source as the abnormal luminance region. The abnormal luminance region detection unit may use a point where the luminance is a discontinuous value as a boundary of the abnormal luminance region.

  The photometric unit may divide the image into matrix cells and measure the luminance of each cell.

  The abnormal luminance region candidate detection unit may detect a cell that exhibits a luminance equal to or higher than the predetermined luminance.

  The abnormal luminance region selection unit may select the abnormal luminance region candidate as the abnormal luminance region when the number of the cells included in the abnormal luminance region candidate is equal to or less than a predetermined number of cells.

  The imaging unit may further include a lens unit that forms an image of the subject and a CCD that receives the image formed by the lens unit and accumulates charges. The photometry unit may integrate the amount of charge accumulated in the CCD for each cell, and calculate the luminance of each cell from a value obtained as a result of the integration.

  A weight storage unit that preliminarily stores a weight corresponding to the position of the cell, and when the cell is included in the abnormal luminance region, the weight corresponding to the cell is reduced and the reduced weight is measured in the cell. And a weighting unit for imparting to the luminance.

  The weight assigning unit may set the weight to zero when the cell is included in the abnormal luminance region and located in a peripheral part of the image. Further, the weight assigning unit may reduce the weight when the cell is included in the abnormal luminance region and is located at the center of the image.

  The weighting unit may divide the weight corresponding to the cell included in the abnormal luminance region by a predetermined numerical value, and change the weight based on a value obtained as a result.

  The predetermined numerical value is a number larger than the weight corresponding to the cell located in the peripheral portion of the image and smaller than the weight corresponding to the cell located in the central portion of the image. May be. The weighting unit changes the weight to zero when the result of the division is less than 1, and sets the weight to a value obtained as a result of the division when the result of the division is 1 or more. It may be changed.

  The predetermined number of cells may be the maximum number of cells that an arbitrary point on the boundary of the cells touches. The cells may be square, and in this case, the number of the predetermined cells may be four.

  According to a second aspect of the present invention, there is provided an exposure control method for controlling exposure, wherein an imaging step for capturing an image of a subject, a photometric step for measuring luminance for each region of the image, and a peripheral portion of the image An abnormal luminance region detection step for detecting an abnormal luminance region having a high local brightness and the luminance for each region of the image excluding the abnormal luminance region are added to calculate an exposure value when the image is captured. And an addition stage.

  The above summary of the invention does not enumerate all the necessary features of the present invention, and sub-combinations of these feature groups can also be the invention.

  Hereinafter, the present invention will be described through embodiments of the invention. However, the following embodiments do not limit the claimed invention, and all combinations of features described in the embodiments are the solution of the invention. It is not always essential to the means.

  FIG. 1 shows a configuration of a digital camera 10 having a function of determining an exposure value based on a luminance level. The exposure value determination mechanism characteristic of the present invention will be described in detail with reference to FIG. The digital camera 10 mainly includes an imaging unit 20, an imaging control unit 40, a processing unit 60, a display unit 100, and an operation unit 110.

  The imaging unit 20 includes a mechanism member and an electrical member related to shooting and imaging. The imaging unit 20 first includes a photographic lens 22 that captures and processes an image, an aperture 24, a shutter 26, an optical LPF (low-pass filter) 28, a CCD 30, and an imaging signal processing unit 32. The photographing lens 22 includes a focus lens, a zoom lens, and the like. With this configuration, a subject image is formed on the light receiving surface of the CCD 30. Charges are accumulated in each sensor element (not shown) of the CCD 30 in accordance with the amount of light of the formed subject image (hereinafter, the charges are referred to as “accumulated charges”). The accumulated charge is read to a shift register (not shown) by a read gate pulse, and sequentially read as a voltage signal by a register transfer pulse.

  Since the digital camera 10 generally has an electronic shutter function, a mechanical shutter such as the shutter 26 is not essential. In order to realize the electronic shutter function, the CCD 30 is provided with a shutter drain via a shutter gate. When the shutter gate is driven, the accumulated charge is swept out to the shutter drain. By controlling the shutter gate, the time for accumulating charges in each sensor element, that is, the shutter speed can be controlled.

  A voltage signal output from the CCD 30, that is, an analog signal, is color-separated into R, G, and B components by the imaging signal processing unit 32, and first, white balance is adjusted. Subsequently, the imaging signal processing unit 32 performs gamma correction, sequentially A / D-converts the R, G, and B signals at a necessary timing, and the resulting digital image data (hereinafter simply referred to as “digital image data”). ) To the processing unit 60.

  The imaging unit 20 further includes a finder 34 and a strobe 36. The finder 34 may be equipped with an LCD (not shown). In this case, various information from the main CPU 62 and the like which will be described later can be displayed in the finder 34. The strobe 36 functions by emitting light when energy stored in a capacitor (not shown) is supplied to the discharge tube 36a.

  The imaging control unit 40 includes a zoom driving unit 42, a focus driving unit 44, an aperture driving unit 46, a shutter driving unit 48, an imaging system CPU 50 that controls them, a distance measuring sensor 52, and a photometric sensor 54. Each of the driving units such as the zoom driving unit 42 has driving means such as a stepping motor. In response to pressing of a release switch 114 described later, the distance measuring sensor 52 measures the distance to the subject, and the photometric sensor 54 measures the subject brightness. The measured distance data (hereinafter simply referred to as “distance data”) and the subject luminance data (hereinafter simply referred to as “luminance data”) are sent to the imaging system CPU 50. The imaging system CPU 50 adjusts the zoom magnification and focus of the photographing lens 22 by controlling the zoom drive unit 42 and the focus drive unit 44 based on photographing information such as a zoom magnification designated by the user.

  The imaging system CPU 50 controls the aperture driving unit 46 and the shutter driving unit 48. An aperture drive unit 46 and a shutter drive unit 48 adjust the aperture amount and open / close the shutter 26, respectively.

  Exposure conditions such as aperture amount and shutter speed are based on the exposure value. The mechanism for determining the exposure value will be described in detail with reference to FIG.

  The imaging system CPU 50 also controls the light emission of the strobe 36 based on the exposure value and simultaneously adjusts the aperture amount of the aperture 26. When the user instructs to capture an image, the CCD 30 starts to accumulate charges, and the accumulated charges are output to the imaging signal processing unit 32 after the shutter time calculated from the exposure value has elapsed.

  The processing unit 60 includes a main CPU 62 that controls the entire digital camera 10, particularly the processing unit 60 itself, a memory control unit 64, a YC processing unit 70, an optional device control unit 74, a compression / decompression processing unit 78, communication, and the like. An I / F unit 80 is included. The main CPU 62 exchanges necessary information with the imaging CPU 50 by serial communication or the like. The operation clock of the main CPU 62 is given from the clock generator 88. The clock generator 88 also provides clocks with different frequencies to the imaging system CPU 50 and the display unit 100, respectively.

  The main CPU 62 is provided with a character generation unit 84 and a timer 86. The timer 86 is backed up by a battery and always counts the date and time. From this count value, information on the shooting date and time information and other time information are given to the main CPU 62. The character generation unit 84 generates character information such as a shooting date and time and a title, and the character information is appropriately combined with the shot image.

  The memory control unit 64 controls the nonvolatile memory 66 and the main memory 68. The non-volatile memory 66 includes an EEPROM (electrically erasable and programmable ROM), a FLASH memory, and the like, and should be retained even when the power of the digital camera 10 is turned off, such as setting information by a user and adjustment values at the time of shipment. Data is stored. In some cases, the non-volatile memory 66 may store a boot program or a system program for the main CPU 62. On the other hand, the main memory 68 is generally composed of a relatively inexpensive memory having a large capacity, such as a DRAM. The main memory 68 has a function as a frame memory for storing data output from the imaging unit 20, a function as a system memory for loading various programs, and other functions as a work area. The nonvolatile memory 66 and the main memory 68 exchange data with each part inside and outside the processing unit 60 via the main bus 82.

  The YC processing unit 70 performs YC conversion on the digital image data, and generates a luminance signal Y and color difference (chroma) signals BY and RY. The luminance signal and the color difference signal are temporarily stored in the main memory 68 by the memory control unit 64. The compression / decompression processor 78 sequentially reads out the luminance signal and the color difference signal from the main memory 68 and compresses them. The data thus compressed (hereinafter simply referred to as “compressed data”) is written to a memory card which is a type of option device 76 via the option device control unit 74.

  The processing unit 60 further has an encoder 72. The encoder 72 receives the luminance signal and the color difference signal, converts them into a video signal (NTSC or PAL signal), and outputs the video signal from the video output terminal 90. When a video signal is generated from data recorded in the option device 76, the data is first supplied to the compression / decompression processing unit 78 via the option device control unit 74. Subsequently, the data that has undergone the necessary expansion processing in the compression / expansion processing unit 78 is converted into a video signal by the encoder 72.

  The option device control unit 74 performs necessary signal generation, logic conversion, voltage conversion, etc. between the main bus 82 and the option device 76 in accordance with the signal specifications recognized by the option device 76 and the bus specifications of the main bus 82. . The digital camera 10 may support a standard I / O card conforming to PCMCIA, for example, in addition to the memory card described above as the optional device 76. In this case, the option device control unit 74 may be configured by a PCMCIA bus control LSI or the like.

  The communication I / F unit 80 performs control such as protocol conversion according to communication specifications supported by the digital camera 10, such as USB, RS-232C, Ethernet, and the like. The communication I / F unit 80 includes a driver IC as necessary, and communicates with an external device including a network via the connector 92. In addition to such standard specifications, a configuration may be adopted in which data is exchanged with an external device such as a printer, a karaoke machine, or a game machine using an original I / F.

  The display unit 100 includes an LCD monitor 102 and an LCD panel 104. They are controlled by a monitor driver 106 and a panel driver 108, which are LCD drivers. The LCD monitor 102 is provided on the back of the camera with a size of about 2 inches, for example, and the current shooting / playback mode, zoom magnification for shooting / playback, battery level, date / time, mode setting screen, subject image, etc. Is displayed. The LCD panel 104 is a small black and white LCD, for example, provided on the top surface of the camera, and simply displays information such as image quality (FINE / NORMAL / BASIC, etc.), strobe light emission / flash inhibition, standard number of shoots, number of pixels, battery capacity, etc. .

  The operation unit 110 includes mechanisms and electric members necessary for the user to set or instruct the operation of the digital camera 10 and its mode. The power switch 112 determines whether to turn on or off the power of the digital camera 10. The release switch 114 has a two-step pushing structure of half-pressing and full-pressing. As an example, AF and AE are locked when pressed halfway, and a captured image is captured when pressed fully, and is recorded in the main memory 68, optional device 76, etc. after necessary signal processing, data compression, and the like. In addition to these switches, the operation unit 110 may accept settings using a rotary mode dial, a cross key, and the like, which are collectively referred to as a function setting unit 116 in FIG. Examples of operations or functions that can be specified by the operation unit 110 include “file format”, “special effect”, “print”, “decision / save”, “display switching”, and the like. The zoom switch 118 determines the zoom magnification.

  The main operation of the above configuration is as follows. First, the power switch 112 of the digital camera 10 is turned on, and power is supplied to each part of the camera. The main CPU 62 reads the state of the function setting unit 116 to determine whether the digital camera 10 is in the shooting mode or the playback mode.

  When the camera is in the shooting mode, the main CPU 62 monitors the half-pressed state of the release switch 114. When the half-pressed state is detected, the main CPU 62 obtains luminance data and distance measurement data from the photometry sensor 54 and the distance measurement sensor 52, respectively. The imaging control unit 40 operates based on the obtained data, and adjustments such as focus and aperture of the taking lens 22 are performed. When the adjustment is completed, a character such as “Standby” is displayed on the LCD monitor 102 to notify the user, and then the release switch 114 is fully pressed. When the release switch 114 is fully pressed, the shutter 26 is closed after a predetermined shutter time, and the accumulated charge in the CCD 30 is swept out to the imaging signal processing unit 32. Digital image data generated as a result of processing by the imaging signal processing unit 32 is output to the main bus 82. The digital image data is temporarily stored in the main memory 68, then processed by the YC processing unit 70 and the compression / decompression processing unit 78, and recorded in the option device 76 via the option device control unit 74. The recorded image is displayed on the LCD monitor 102 in a frozen state for a while, and the user can know the captured image. This completes a series of shooting operations.

  On the other hand, when the digital camera 10 is in the playback mode, the main CPU 62 reads the last photographed image from the main memory 68 via the memory control unit 64 and displays it on the LCD monitor 102 of the display unit 100. In this state, when the user instructs “forward” or “reverse” on the function setting unit 116, images taken before and after the currently displayed image are read and displayed on the LCD monitor 102.

  FIG. 2 shows a schematic functional block of the exposure value determination unit 200 that is characteristic of the present invention. As an example, the exposure value determination unit 200 can be realized by cooperation of the imaging control unit 40 and the main CPU 62 in FIG. 1 and programs stored or loaded in the main memory 68 and the nonvolatile memory 66. When the main CPU 62 has a built-in memory, a necessary program may be stored in the memory and various functions may be realized as firmware. In FIG. 2, each function is described as a unitary configuration, but these are not necessarily physically combined and need not be. For example, the exposure value determination unit 200 may not have the weight storage unit 222, and in this case, information held by the weight storage unit 222 may be input from the outside. The design for realizing the function of the exposure value determining unit 200 in the digital camera 10 has a considerable degree of freedom.

  The exposure value determination unit 200 includes a photometric sensor 54, a buffer memory 202, a calculation unit 204, an absolute reference value storage unit 208, a product-sum circuit 206, an abnormal luminance region detection unit 210, a weight storage unit 222, and a weighting unit 224. .

  The photometric sensor 54 divides the image formed by the photographing lens 22 into 64 cells in a matrix and measures the luminance for each cell. The photometric sensor 54 stores the luminance data indicating the luminance of each cell in the buffer memory 202 in association with the position data indicating the cell position. The position data may be data indicating coordinates in the image, or may be given as a position data by giving consecutive numbers in the vertical or horizontal direction to the cells arranged in a matrix. In any case, the position data may be data that can specify the position of the cell, and the data content is not limited to the above.

  Luminance data and position data are associated by a file name. As another form, it may be associated with information unique to data such as luminance data and position data ID, or the corresponding information may be stored in one file. In any case, it is only necessary to store the luminance data and the position data in association with each other, and the degree of freedom in design for realizing this is great.

  The absolute reference value storage unit 208 stores absolute reference value data indicating a reference luminance that is regarded as an abnormal luminance region. The absolute reference value is an absolute value of luminance. The arithmetic unit 204 extracts the luminance data of all the cells stored in the buffer memory 202, calculates the luminance average for all the cells, and obtains a relative reference value that is larger than the luminance average by a predetermined value. The arithmetic unit 204 also extracts absolute reference value data from the absolute reference value storage unit 208 and determines a threshold value that is regarded as abnormal luminance based on the absolute reference value and the relative reference value. For example, when the absolute reference value is lower than the relative reference value, the absolute reference value may be the threshold value, and when the relative reference value is lower than the absolute reference value, the relative reference value may be the threshold value. The calculation unit 204 sends threshold value data indicating a threshold value to the high luminance cell detection unit 212.

  In this way, the threshold value is determined in consideration of the relative reference value based on the average luminance of the entire image in addition to the absolute reference value. Therefore, the optimum exposure value for the entire image can be determined even for an image whose luminance tends to be low or high.

  The abnormal luminance area detection unit 210 detects an abnormal luminance area having a locally high luminance such as a light source. The abnormal luminance region detection unit 210 includes an abnormal luminance region candidate detection unit 214 and an abnormal luminance region selection unit 216.

  The abnormal luminance region candidate detection unit 214 extracts all luminance data stored in the buffer memory 202 and receives threshold data from the calculation unit 204. The abnormal brightness area candidate detection unit 214 detects a high brightness cell that exhibits brightness higher than the threshold value, and uses the position data associated with the brightness data of the detected high brightness cell as high brightness position data from the buffer memory 202. Extract. The abnormal luminance region candidate detection unit 214 detects a plurality of high luminance position data in which the cell positions are continuous in the image. The abnormal luminance region candidate detection unit 214 sets the region occupied by these high luminance position data as the abnormal luminance region candidate. The high-luminance position data for which the high-luminance position data does not exist with respect to the continuously arranged cells is an abnormal luminance region candidate in the area indicated by the high-luminance position data itself, that is, the area occupied by one cell indicated by the high-luminance position data. To do. The abnormal luminance region candidate detection unit 214 sends abnormal luminance region candidate data indicating the number of cells included in the abnormal luminance region candidate and the position of each cell to the abnormal luminance region selection unit 216. In this manner, since a cell having a predetermined luminance abnormality is detected, it is possible to faithfully cut out only the abnormal luminance region.

  The abnormal luminance region selection unit 216 receives abnormal luminance region candidate data. The abnormal luminance region selection unit 216 stores the maximum number of cells 4 in advance. The abnormal luminance region selection unit 216 selects an abnormal luminance region candidate having four or less cells from the abnormal luminance region candidate data as an abnormal luminance region. The abnormal luminance region selection unit 216 sends abnormal luminance region position data indicating the positions of the cells included in the selected abnormal luminance region to the weighting unit 224. In this way, the brightness of relatively small cells is measured, and the area having a predetermined number of cells or less is defined as an abnormal brightness area. Therefore, an area where high brightness is dominant and an abnormal brightness area where brightness is locally high Can be distinguished.

  A weight reference value serving as a weight reference is given to each cell, and the weight storage unit 222 stores weight reference value data indicating the weight reference value in association with the position data of each cell. The size of the weight reference value depends on the position of the cell in the image.

The weighting unit 224 extracts the weight reference value data stored in the weight storage unit 222 and receives abnormal luminance region position data from the abnormal luminance region selection unit 216. The weight assigning unit 224 changes the weight reference value to a weight to be weighted to the luminance measured in each cell. That is, the weight Wi is calculated by performing the calculation of (Equation 1) for each cell.

In Equation 1, w _i is a weight set in advance for each cell i, and AL _i is a weight reduction coefficient for each cell i. When cell i is not included in the abnormal luminance region, 1 is assigned to AL _i . When the cell i is included in the abnormal luminance region, the weight value is larger than the weight value given to the peripheral cell of the image and smaller than the weight value given to the central cell of the image. The number is assigned to AL _i . For example, 3 may be substituted for AL _i .

According to (Expression 1), when the calculated Wi is less than 1, the weight of the cell i is changed to 0, and when Wi is 1 or more, the weight of the cell i is changed to Wi. Therefore, when a cell included in the abnormal luminance region is a cell to which a weight reference value larger than AL _i is given, the weight weighted to the luminance is reduced, and the cell included in the abnormal luminance region is smaller than AL _i. If the cell is given a weight reference value, the brightness of this cell can be excluded from the calculation of the exposure value. The weight assigning unit 224 also sends weight data indicating the changed weights of all the cells and the cell positions corresponding to the weights to the product-sum circuit 206.

  The product-sum circuit 206 extracts luminance data of all cells from the buffer memory 202. The product-sum circuit 206 also receives weight data from the weighting unit 224. The product-sum circuit 206 adds luminance and determines an optimum exposure value when the imaging unit 20 captures this image. At this time, the luminance of each cell is multiplied by the weight given to each cell. That is, the luminance of each cell is multiplied by a weight, and the integral of all cells with the weighted luminance is calculated. The product-sum circuit 206 sends the calculated value to the exposure condition determination unit 226. The exposure condition determination unit 226 determines exposure conditions such as an aperture value and a shutter speed when the imaging unit 20 captures images based on the received values.

The calculation performed by the weighting unit 224 and the product-sum circuit 206 is expressed by (Expression 2). In (Expression 2), EV represents an exposure value, and ev _i represents the luminance of each cell i. In this way, the weight reference value given in advance for each cell is divided by AL _i to change the weight value, and the product sum of the changed weight and the measured value is calculated for all cells. Accordingly, it is possible to calculate an optimum exposure value for the image in consideration of the abnormal luminance region.

  FIG. 3 shows an image 300 divided into regularly arranged rectangular cells. In this case, the number of cells that an arbitrary point on the boundary of one cell 302 contacts is maximum at the vertex position of the cell, and the maximum number of cells is four. Therefore, in this case, the abnormal luminance region selection unit 216 (FIG. 2) stores the maximum number of cells 4 in advance. The abnormal luminance area selection unit 216 also selects an abnormal luminance area candidate including four or less cells as an abnormal luminance area.

  A weight reference value is given to each of the 64 cells constituting the image 300. A cell closer to the center point 320 is given a larger weight reference value. In order from the end of the image 300, the weight reference value 1 for each cell in the first area 310, the weight reference value 2 for each cell in the second area 312 and the weight reference value for each cell in the third area 314 A weight reference value of 5 is given to each cell in the fourth and fourth regions 316. Therefore, the luminance in the region near the center point 320 greatly contributes to the calculation of the exposure value. Since the main subject is often placed in the center, the optimal exposure for the main subject is set by setting the luminance in the region near the center point 320 to greatly contribute to the exposure value. The value can be determined.

The weight applying unit 224 (FIG. 2), since stores 3 as AL _i to an abnormal luminance area, _{W i} of the cell 302 of the abnormal luminance part present in the peripheral portion 306 has a value of less than 1 , _{W i} of the cell 302 of the abnormal luminance part present in the center portion 304 is a value of 1 or more. That is, the weight can be reduced for the cells 302 in the abnormal luminance region existing in the central portion 304, and the weight can be made zero for the cells 302 in the abnormal luminance region existing in the peripheral portion 306. it can. The weight reference value given to each cell and the number given as AL _i for the abnormal luminance region by the weight assigning unit 224 can be arbitrarily set.

  FIG. 4 shows an image 300 formed by the photographing lens 22. As described above, when a light source exists in the peripheral portion 306, the average luminance of the entire image 300 is increased by the abnormal luminance region 330. Therefore, when the exposure value is calculated based on the luminance average, an exposure value that is too small for the area of the person who is the main subject is calculated. However, according to the present embodiment, the luminance of the cell included in the abnormal luminance region 330 located in the peripheral portion 306 is excluded when calculating the exposure value, so that it is possible to photograph with the optimal exposure value for the person. . In other words, it is possible to prevent the exposure of the central portion 304 where the main subject is relatively disposed from becoming unnecessarily small.

  Further, although the weight of the cell in the abnormal luminance region 330 existing in the central portion 304 is reduced in weight, it is not excluded. Therefore, for example, even when the main subject includes the abnormal luminance region 330 as in the case where the person is directly exposed to light, the optimum exposure value for the main subject can be calculated.

  FIG. 5 is a flowchart showing the operation of the digital camera 10 when taking an image. When shooting starts, the shooting lens 22 forms an image 300 (S100). Next, the photometric sensor 54 divides the image into 64 cells and measures the luminance for each cell (S102). Next, the abnormal luminance region detection unit 210 detects an abnormal luminance region (S104). Next, the weight assigning unit 224 calculates a weight to be weighted to the luminance of each cell from the weight reference value based on the weight reference value data and the abnormal luminance region position data (S106). Next, the weighting unit 224 multiplies the measured luminance for each cell by the weight calculated for each cell. Next, the exposure value determination unit 226 integrates the weighted luminance of each cell for all the cells to calculate an exposure value. Next, the exposure condition determination unit 226 determines an exposure condition for this image (S108). Next, the image 300 is photographed under the determined exposure conditions (S110). This completes the image shooting. In this way, since the brightness is adjusted for each shooting, an image can be shot with an optimal exposure value for each image.

  FIG. 6 is a flowchart showing a detailed operation of the exposure value determination unit 200 in the abnormal luminance region detection step (S104) of FIG. The calculation unit 204 calculates the average luminance of all the cells 302 included in the image 300 from the luminance data stored in the buffer memory 202 (S200). Next, the calculation unit 204 determines a threshold value to be regarded as an abnormal luminance region based on the absolute reference value and the relative reference value (S202). Next, the abnormal brightness area candidate detection unit 214 detects a high brightness cell having brightness higher than the threshold value, and extracts position data corresponding to the cell from the buffer memory 202 as high brightness position data. Next, consecutively arranged high luminance cells are detected, and an area occupied by the high luminance cells is set as an abnormal luminance area candidate. In addition, for a cell in which there are no continuously arranged cells, the cell itself, that is, one cell is set as an abnormal luminance region candidate (S204). Next, the abnormal luminance region selection unit 216 selects, as the abnormal luminance region, an abnormal luminance region candidate having four or less cells occupied by the region from among the abnormal luminance region candidates received from the abnormal luminance region candidate detection unit 214 ( S206).

  In this way, since the area of the abnormal luminance region is determined in advance, when a region of a predetermined area or more is high luminance, it is recognized as an image in which high luminance is dominant, and the high luminance region is below the predetermined area. In this case, it can be recognized as an abnormal luminance region. That is, it is possible to determine whether high luminance is a dominant region or an abnormal luminance region for cells having the same luminance. Therefore, when calculating the exposure value, reduce the overall brightness for areas where high brightness is dominant, and for abnormal brightness areas, make sure that the brightness of the abnormal brightness area does not affect the overall brightness. The luminance contribution in the luminance region can be reduced.

  FIG. 7 shows another shape of the cell that is measured by the photometric sensor 54 of the digital camera 10. Image 300 is divided into triangular cells 340. In this case, the maximum number of triangular cells 340 that an arbitrary point on the boundary of the triangular cell 340 contacts is six. Therefore, the abnormal luminance area selection unit 216 stores the maximum number of cells 6 and selects an abnormal luminance area candidate having six or less cells as the abnormal luminance area from the abnormal luminance area candidates received from the abnormal luminance area candidate detection unit 214. .

  FIG. 8 shows still another shape of the cell that is measured by the photometric sensor 54 of the digital camera 10. Image 300 is divided into hexagonal cells 342. In this case, the maximum number of hexagonal cells 342 that an arbitrary point on the boundary of the hexagonal cells 342 contacts is three. Therefore, the abnormal luminance region selection unit 216 stores the maximum number of cells 3 and selects an abnormal luminance region candidate having three or less cells as the abnormal luminance region from the abnormal luminance region candidates received from the abnormal luminance region candidate detection unit 214. To do.

  In another embodiment, the abnormal luminance region candidate detection unit 214 detects a high luminance cell, detects a point where the luminance becomes discontinuous based on luminance data of a cell adjacent to the high luminance cell. Also good. In this case, the point where the luminance is discontinuous is set as the boundary of the abnormal luminance region candidate. The abnormal luminance region candidate detection unit 214 also sets the number of cells up to the cell including the boundary as the number of cells included in the abnormal luminance region candidate. The abnormal luminance region candidate detection unit 214 sends abnormal luminance region candidate data indicating the number of cells included in the abnormal luminance region and the position thereof to the abnormal luminance region selection unit 216. Also in this embodiment, it is possible to detect an abnormal region faithfully.

  In the first embodiment, the present invention has been described using the example of the digital camera 10. However, the present invention can also be used in a video camera that captures moving images. Since the overall configuration of the video camera is substantially the same as the overall configuration of the digital camera 10 described in the first embodiment, description thereof is omitted. However, in the case of a video camera, the option device 76 in FIG. 1 may be a video tape. The other configuration and operation of the video camera are substantially the same as the configuration and operation of the digital camera 10 according to the first embodiment described with reference to FIGS.

  Although the embodiments have been described above, the technical scope of the present invention is not limited to these descriptions. It will be understood by those skilled in the art that various modifications or improvements can be added to these embodiments.

  As such a first modification, in the present embodiment, the imaging apparatus is the digital camera 10 and the video camera, but may be a still camera, and is a digital that can capture both still images and moving images. It may be a camera. In either case, the exposure value determining unit 200 is mounted, and the exposure value is calculated by the exposure value determining unit 200.

  As a second modification, in the present embodiment, the luminance of each cell is measured by the photometric sensor 54. Instead of the photometric sensor, the charge amount accumulated in the CCD 30 is integrated for each cell, The luminance of each cell may be calculated using the value obtained as a result.

  As a third modification, in this embodiment, the image is divided into cells having a predetermined area, but the cells may be one element of the CCD.

  As a fourth modification example, in this embodiment, the weight assigning unit 224 performs an operation of extracting all data from the weight storage unit 222 and changing the weight, but the weight assigning unit 224 The weights may be changed only for the cells included in the luminance region, and other weight data may be sent to the product-sum circuit 206 as it is.

  As a fifth modified example, in the present embodiment, the maximum number of cells in the abnormal luminance region is the maximum number of cells that are in contact with any point on the cell boundary, but the maximum number of cells is May be set to a large number.

  As a sixth modification, in the present embodiment, the photometric sensor 54 measures the luminance for each cell of the same size arranged in a matrix, but the cell size may not be unified. Good. For example, the cells in the peripheral part 306 may be larger than the cells in the central part 304.

  As a seventh modification, in the present embodiment, the abnormal luminance region candidate detection unit 214 determines a region having a predetermined area or less as the abnormal luminance region, but the abnormal luminance region candidate detection unit 214 has a predetermined Different areas may be stored for the abnormal luminance regions located in the central part 304 and the peripheral part 306 of the image.

  As an eighth modification example, the abnormal luminance region detection unit 210 according to the present embodiment detects the abnormal luminance region 330 from all the cells 302 included in the image 300. Alternatively, the abnormal luminance region 330 may be detected only from the peripheral portion 306.

As a ninth modification example, in the present embodiment, the weight is set higher in the region closer to the center point 320, but the weight of the region where the main subject is likely to be arranged only needs to be higher. The setting is not limited to this. For example, in the calculation for determining the exposure value in the weighting unit 224 and the product-sum circuit 206, when the abnormal luminance region 330 is located in the central portion 304, the luminance of the cells included in the abnormal luminance region 330 may be excluded. For example, when the abnormal luminance region 330 is located in the peripheral portion 306, the luminance of the cells included in the abnormal luminance region 330 may be taken into account. Further, the number and arrangement of cells in the image, the value of weight, and the value of AL _i are not limited to the present embodiment, and these settings have a considerable degree of freedom.

  As is apparent from the above description, according to the present invention, the exposure value can be determined based on the luminance level.

1 is an overall configuration diagram of a digital camera 10. FIG. 4 is a functional block diagram illustrating functions of an exposure value determining unit 200. FIG. It is a figure which shows the image 300 divided | segmented into the cell arrange | positioned regularly. It is a figure which shows the image 300 imaged by the imaging lens. 4 is a flowchart illustrating an operation of the digital camera 10 when an image 300 is captured. It is a flowchart which shows the detailed operation | movement of the exposure value determination part 200 in S104 of FIG. It is a figure which shows the other shape of the cell which the photometry sensor 54 of the digital camera 10 measures. It is a figure which shows other shape of the cell which the photometry sensor 54 of the digital camera 10 measures.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Digital camera 20 ... Imaging unit 22 ... Shooting lens 24 ... Aperture 26 ... Shutter 28 ... Optical LPF 30 ... CCD 32 ... Imaging signal processing part 34 ... Finder 36 ... Strobe 36a ... Discharge tube 40 ... Imaging control unit 42 ... Zoom drive Unit 44: Focus drive unit 46 ... Aperture drive unit 48 ... Shutter drive unit 50 ... Imaging system CPU 52 ... Distance measuring sensor 54 ... Photometric sensor 60 ... Processing unit 62 ... Main CPU 64 ... Memory control unit 66 ... Non-volatile memory 68 ... Main memory 70 ... YC processing unit 72 ... Encoder 74 ... Optional device control unit 76 ... Optional device 78 ... Compression / decompression processing unit 80 ... Communication I / F unit 82 ... Main bus 84 ... Character generation unit 86 ... Timer 8 DESCRIPTION OF SYMBOLS ... Clock generator 90 ... Video output terminal 92 ... Connector 100 ... Display unit 110 ... Operation unit 200 ... Exposure value determination part 202 ... Buffer memory 204 ... Calculation part 206 ... Sum-of-products circuit 208 ... Absolute reference value memory | storage part 210 ... Abnormal brightness Area detection unit 214 ... abnormal luminance region candidate detection unit 216 ... abnormal luminance region selection unit 218 ... maximum cell number storage unit 222 ... weight storage unit 224 ... weight assignment unit 226 ... exposure condition determination unit 300 ... image 302 ... cell 304 ... center Part 306 ... Peripheral part 310 ... First area 312 ... Second area 314 ... Third area 316 ... Fourth area 320 ... Center point

Claims (7)

An imaging unit for capturing an image;
A photometric unit that divides the image into a plurality of cells and measures the luminance of each cell;
An abnormal luminance region detecting unit for detecting an abnormal luminance region having high local luminance from the image;
A weight storage unit that stores in advance a weight corresponding to the position of the cell;
When the cell is included in the abnormal luminance region, a weighting unit that changes the weight corresponding to the cell to a smaller weight;
Multiplying the luminance measured by the photometry unit by the weight stored in the weight storage unit or the weight changed by the weighting unit, and adding the calculated value to take an image An imaging device comprising a circuit. The abnormal luminance region detection unit is
An abnormal luminance region candidate detection unit that detects, as an abnormal luminance region candidate, an area occupied by a cell having a predetermined luminance or higher in the image;
The imaging according to claim 1, further comprising: an abnormal luminance region selection unit that selects the abnormal luminance region candidate as the abnormal luminance region when the number of the cells included in the abnormal luminance region candidate is equal to or less than a predetermined number of cells. apparatus. The imaging unit is
A lens unit that forms an image of the subject;
A CCD that receives the image formed by the lens unit and accumulates charges;
The imaging device according to claim 1, wherein the photometry unit calculates the luminance for each cell by integrating the charge amount accumulated in the CCD for each cell.   The weighting unit changes a weight to zero when the cell is included in the abnormal luminance region and located in a peripheral portion of the image, and the cell is included in the abnormal luminance region and the center of the image. The imaging device according to any one of claims 1 to 3, wherein the weight is reduced when the unit is located in a portion.   The weighting unit divides a weight corresponding to the cell included in the abnormal luminance region by a predetermined numerical value, and changes the weight based on a value obtained as a result of the division. The imaging device described in 1. The predetermined numerical value is a number that is larger than a weight corresponding to the cell located in a peripheral part of the image and smaller than a weight corresponding to the cell located in a central part of the image;
The weighting unit changes the weight to zero when the result of the division is less than 1, and changes the weight to a value obtained as a result of the division when the result of the division is 1 or more. The imaging device according to claim 5. An imaging stage for capturing an image;
A photometric step of dividing the image into a plurality of cells and measuring the brightness of each cell;
An abnormal luminance region detection step of detecting an abnormal luminance region having high local brightness from the image;
When the cell is included in the abnormal luminance region, a weighting step of changing the weight corresponding to the position of the cell stored in advance by the weight storage unit to a smaller weight,
Multiplying the luminance for each cell measured in the photometry step by the weight stored in correspondence with the position of the cell by the weight storage unit or the weight changed in the weighting step, and adding the image. An exposure control method comprising: an addition stage for calculating an exposure value when shooting.

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