JP2007053617A - Exposure value operation method and imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent exposure from being largely deviated from appropriate exposure for a principal subject even when contrast between the principal subject and a background is extremely high. <P>SOLUTION: An image division part 55a divides image data output from an A/D 42 into a plurality of small areas. A luminance operation part 55b calculates a subject luminance value of each small area. An exposure operation part 55c multiplies each subject luminance value by a weight coefficient to operate a weighted average and thereby calculates an exposure value of image data. Weight coefficients are set by a weight coefficient operation circuit 56. The weight coefficient operation circuit 56 detects a maximum value of subject luminance values and calculates difference values from the maximum value per small area and sets the weight coefficients on the basis of the difference values. The difference values are larger for parts having lower subject luminance values, and the weight coefficients are larger in proportion to the difference values. Thus exposure can be adapted to the principal subject having a low subject luminance value even when the principal subject is extremely darker than the background. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention divides an imaging screen represented by image data into a plurality of small areas, calculates subject luminance values for each small area, and calculates an exposure value for the image data based on each subject luminance value The present invention relates to a calculation method and an imaging apparatus using the exposure value calculation method.

  As one of imaging apparatuses, a digital camera that converts a subject image captured by a solid-state imaging device such as a CCD into digital image data and stores the digital image data in a storage medium such as a built-in memory or a memory card is widely used. In such a digital camera, automatic exposure adjustment for automatically determining a shutter speed, an aperture value, and the like is performed by measuring an image brightness from image data and calculating an appropriate exposure value.

As photometry methods for automatic exposure adjustment, for example, average photometry and center-weighted photometry are known (see Patent Document 1). Average photometry is a photometric method that calculates the average brightness of the entire image as an appropriate exposure value. On the other hand, center-weighted metering assumes that the main subject is near the center of the image, and after dividing the image into a plurality of small areas and calculating the brightness for each small area, This is a photometric method for calculating an appropriate exposure value by increasing the weight of a region. In this center-weighted metering, even when the contrast between the main subject and the background is large, the main subject is more easily exposed than the average metering.
Japanese Patent Application Laid-Open No. 07-087372

  However, if the contrast between the main subject and the background is extremely large, for example, in a backlight scene or in a night scene with a spotlight, the exposure of the main subject is possible even if center-weighted metering is used. It was difficult to suppress under-exposure and over-exposure.

  The present invention has been made in view of the above problems, and an object of the present invention is to prevent the exposure from being largely deviated from the main subject even when the contrast between the main subject and the background is extremely large.

  In order to achieve the above object, an exposure value calculation method of the present invention represents a data acquisition step of acquiring image data corresponding to the subject image from an image sensor that captures the subject image transmitted through the imaging lens, and the image data represents A dividing step for dividing the imaging screen into a plurality of small areas; a luminance calculating step for calculating a subject luminance value for each of the small areas; and for each calculation so that the smaller area having the lower subject luminance value has a higher weight. A weighting factor calculation step for setting a weighting factor, and multiplying each subject luminance value by the calculation weighting factor set for each of the small areas to obtain a weighted average, thereby calculating the exposure value of the image data It is characterized by calculating.

  The weighting factor calculating step includes a step of detecting a maximum value of each subject luminance value, and subtracting each subject luminance value from the maximum value to obtain a difference value from the maximum value for each small region. A step of calculating, a step of inputting each of the difference values to a correction function for conversion so that a larger portion of the input value becomes larger, obtaining an output value according to the correction function, and weighting of a central portion of the imaging screen Preferably, the method includes a step of multiplying each of the small areas by a weight factor of a center weight set in advance for each of the small regions and each of the output values, and setting the multiplication result as the weighting factor for each calculation. .

  Each difference value is preferably normalized to a value corresponding to the input range of the correction function before being input to the correction function.

  Further, after the luminance calculation step, an average luminance value calculating step for calculating an average luminance value of the subject luminance values and a determining step for determining whether or not the average luminance value is equal to or greater than a predetermined value are performed. When it is determined that the average luminance value is equal to or greater than a predetermined value, the weighting factor calculation step is performed. When it is determined that the average luminance value is equal to or less than the predetermined value, the center of the imaging screen is determined. It is preferable that the exposure value is calculated using a center-weighted weighting factor set in advance in each of the small regions so as to increase the weighting of the portion, as the calculation weighting factor.

  The exposure value calculation method of the present invention includes a data acquisition step of acquiring image data corresponding to the subject image from an image sensor that captures the subject image that has passed through the imaging lens, and a plurality of imaging screens represented by the image data. A division step for dividing into small areas, a luminance calculation step for calculating subject luminance values for each of the small areas, and setting the weighting factors for each calculation so that the smaller areas with higher subject luminance values have higher weights. A weighting factor calculation step, wherein the exposure value of the image data is calculated by multiplying the subject luminance value by a calculation weighting factor set for each small area and taking a weighted average. Also good.

  In this case, the weighting factor calculation step includes a step of detecting a minimum value of each subject luminance value, and subtracting the minimum value from each subject luminance value to obtain a difference value from the minimum value for each small region. Obtaining the output value corresponding to the correction function by inputting each difference value into a correction function for converting the large input value portion to be larger, and weighting the central portion of the imaging screen. Each of the small regions is multiplied by a weighting factor of a center weight set in advance for each of the small regions and the output value, and the multiplication result is set as the weighting factor for each calculation. preferable.

  Each difference value is preferably normalized to a value corresponding to the input range of the correction function before being input to the correction function.

  Further, after the luminance calculation step, an average luminance value calculating step for calculating an average luminance value of the subject luminance values and a determining step for determining whether or not the average luminance value is equal to or greater than a predetermined value are performed. When the average luminance value is determined to be less than or equal to a predetermined value, the weighting coefficient calculation step is performed. When the average luminance value is determined to be equal to or greater than the predetermined value, the center of the imaging screen is determined. It is preferable that the exposure value is calculated using a center-weighted weighting factor set in advance in each of the small regions so as to increase the weighting of the portion, as the calculation weighting factor.

  The exposure value calculation method of the present invention includes a data acquisition step of acquiring image data corresponding to the subject image from an image sensor that captures the subject image that has passed through the imaging lens, and a plurality of imaging screens represented by the image data. A division step of dividing into small areas, and a luminance calculation step of calculating a subject luminance value for each of the small areas, and multiplying each of the subject luminance values by a weighting factor set for each of the small areas, the weighted average A plurality of exposure value calculation steps for calculating a plurality of the exposure values using a plurality of weighting factors having different weights when calculating the exposure value of the image data, and an average luminance of the subject luminance values An average luminance value calculating step for calculating a value and a conversion function provided for each of the exposure values to obtain a combination ratio of the exposure values according to the average luminance value. Steps and, the may be those including the optimum exposure value calculation step to determine the one optimum exposure values from the exposure value and the each combination ratio.

  At this time, the plurality of weighting factors are set such that at least the first weighting factor set to increase the weighting in the small region with the lower subject luminance value and the weighting in the small region with the higher subject luminance value. It is preferable that the second weighting coefficient set so as to be equal to the third weighting coefficient set so that the weighting is increased in the small area in the central portion of the imaging screen.

  Further, the first weighting coefficient detects a maximum value of each subject luminance value, subtracts each subject luminance value from the maximum value, and obtains a difference value from the maximum value for each small region, The difference value is input to a correction function that converts the larger input value to be larger, and an output value corresponding to the correction function is obtained. The preset third weighting factor and each output value And the second weighting factor detects the minimum value of each subject luminance value, subtracts the minimum value from each subject luminance value, and sets the minimum value for each small region. The difference value is obtained from the input value, and each difference value is input to a correction function that converts the larger input value to be larger, and an output value corresponding to the correction function is obtained. Multiplying the weighting factor by each output value It is preferable to set me.

  The imaging device of the present invention includes an imaging device that captures a subject image that has passed through an imaging lens and outputs image data corresponding to the subject image, a diaphragm that adjusts the amount of incident light on the imaging device, and the image Dividing means for dividing the imaging screen represented by the data into a plurality of small areas, luminance calculating means for calculating a subject luminance value for each of the small areas, and calculating an exposure value of the image data based on each of the subject luminance values Exposure calculation means, and exposure control means for controlling at least one of the aperture value of the aperture and the exposure time of the image sensor based on the calculated exposure value, wherein the exposure calculation means is one of the above The exposure value is calculated using an exposure value calculation method.

  According to the present invention, the weighting factor for each calculation is set so that the smaller the region with a lower subject luminance value is, the larger the weighting factor for each operation. Even when it becomes dark, the exposure is adjusted to the main subject having a low subject luminance value, so that it is possible to prevent the exposure from being greatly deviated from the main subject. Also, if the weighting factor for each calculation is set so that the smaller the area with a higher subject luminance value, the higher the weight, the main subject will become extremely bright with respect to the background, such as a shooting scene with a spotlight applied at night. Even in such a case, since the exposure is adjusted to the main subject having a high subject luminance value, it is possible to prevent the exposure from being largely deviated from the main subject.

  Furthermore, using a plurality of weighting factors including a weighting factor set so that weighting is increased in a small region with a low subject luminance value, and a weighting factor set so that weighting is increased in a small region with a high subject luminance value. By calculating multiple exposure values and combining each of these exposure values to determine one optimal exposure value, whether the main subject is extremely dark or extremely bright against the background , It is possible to prevent the exposure from being largely deviated from the main subject.

  FIG. 1 and FIG. 2 show the external appearance of a digital camera (imaging device) 2. As shown in the perspective view of FIG. 1, a lens barrel 11 that holds an imaging lens 10 is provided on the front surface of the digital camera 2. On the upper surface of the digital camera 2, a release button 12, a power switch 13, and a mode dial 14 are provided. Further, a memory card slot (not shown) in which a memory card 52 (see FIG. 3) is detachably loaded is provided on the side surface, and the lid 15 covers this memory card slot.

  As is well known, the power switch 13 is used when turning on / off the power of the digital camera 2. The digital camera 2 can select a still image shooting mode for shooting still images, a movie shooting mode for shooting movies, a playback mode for displaying captured images on the LCD 22, and a setting mode for performing various settings. . Switching between these modes is performed by rotating the mode dial 14. In the moving image shooting mode, along with shooting of moving images, surrounding sounds are recorded via a microphone (not shown).

  The release button 12 is a two-stage push switch. After the framing of the subject by the LCD 22, when the release button 12 is lightly pressed (half-pressed), various shooting preparation processes such as automatic exposure adjustment (AE) and automatic focus adjustment (AF) are performed. In this state, when the release button 12 is pressed once more (fully pressed), the imaging signal for one screen on which the imaging preparation processing has been performed is converted into image data. The converted image data is stored in the memory card 52 after, for example, various image processing and compression processing are applied.

  FIG. 2 is a plan view of the digital camera 2 as viewed from the back. A finder eyepiece window 21, a liquid crystal display (LCD) 22, and an operation unit 23 that constitute an electronic viewfinder are provided on the back surface of the digital camera 2. The LCD 22 displays, for example, captured images, so-called through images, and various menu screens. The operation unit 23 is a zoom operation button 24 that changes the zoom lens 30 (see FIG. 3) of the image pickup lens 10 to the wide-angle side and the telephoto side, when the menu screen is displayed on the LCD 22, and when the selection content is determined. The menu button 25 is operated, and the cross key 26 is used to move the cursor in the menu screen.

  FIG. 3 is a block diagram schematically showing the internal configuration of the digital camera 2. The imaging lens 10 includes a zoom lens 30, a diaphragm 31, and a focus lens 32 arranged along the optical axis L. A lens motor 33 is connected to the zoom lens 30. The lens motor 33 moves the zoom lens 30 to the wide angle side or the telephoto side in conjunction with the operation of the zoom operation button 24. An iris motor 34 is connected to the diaphragm 31. The iris motor 34 adjusts the amount of light incident from the zoom lens 30 by changing the aperture area (aperture value) of the diaphragm 31 during the photographing preparation process when the release button 12 is half-pressed. A lens motor 35 is connected to the focus lens 32. The lens motor 35 moves the focus lens 32 to the close side or the infinity side in response to zooming of the zoom lens or half-pressing of the release button 12.

  Each motor 33, 34, 35 is connected to a motor driver 36. The motor driver 36 is connected to a CPU 37 that comprehensively controls the digital camera 2, and transmits drive pulses to the motors 33, 34, and 35 based on control signals from the CPU 37. Each of the motors 33, 34, and 35 rotates the rotation shaft according to the drive pulse. As each motor 33, 34, 35, for example, a stepping motor is used.

  Behind the imaging lens 10 is a CCD (imaging device) 38 that captures a subject image that has passed through the imaging lens 10. A timing generator (TG) 39 controlled by the CPU 37 is connected to the CCD 38, and a shutter speed (exposure time) of the electronic shutter is determined by a timing signal (clock pulse) input from the TG 39. That is, the CPU 37 can control the aperture value of the aperture 31 and the exposure time of the CCD 38, and corresponds to the exposure control means described in the claims.

  The imaging signal output from the CCD 38 is input to a correlated double sampling circuit (CDS) 40. The CDS 40 removes noise from the imaging signal by performing correlated double sampling. The amplifier (AMP) 41 receives the imaging signal from which noise has been removed from the CDS 40, and amplifies the imaging signal with a gain corresponding to the imaging sensitivity set by the CPU 37. The A / D converter (A / D) 42 receives the amplified imaging signal from the AMP 41, digitally converts it, and outputs it as image data.

  The image input controller 43 is connected to the CPU 37 via the bus 44, and controls each part of the CCD 38, the CDS 40, the AMP 41, and the A / D 42 in accordance with a control command from the CPU 37. The image data output from the A / D 42 is temporarily recorded in the SDRAM 45.

  The image signal processing circuit 46 reads the image data from the SDRAM 45, performs various image processing such as gradation conversion, white balance correction, and γ correction processing, and records the image data in the SDRAM 45 again. The YC conversion processing circuit 47 reads out the image data subjected to various processes by the image signal processing circuit 46 from the SDRAM 45, and converts it into a luminance signal Y and color difference signals Cr and Cb.

  The VRAM 48 is a memory for outputting a through image to the LCD 22, and stores image data that has passed through the image signal processing circuit 46 and the YC conversion processing circuit 47. The VRAM 48 has a memory for two frames so that image data can be written and read in parallel. The image data stored in the VRAM 48 is converted into an analog composite signal by the LCD driver 49 and displayed as a through image on the LCD 22.

  The compression / decompression processing circuit 50 compresses the image data YC converted by the YC conversion processing circuit 47 in a predetermined compression format such as TIFF or JPEG. The compressed image data is stored in the memory card 52 via the media controller 51.

  In addition to the release button 12 and the operation unit 23, an EEPROM 53 is connected to the CPU 37. The EEPROM 53 stores various control programs and setting information. The CPU 37 reads these pieces of information from the EEPROM 53 to the SDRAM 45, which is a working memory, and executes various processes.

  Furthermore, the bus 44 detects an AF detection circuit 54 that detects the focal position of the imaging lens 10 that is suitable for photographing and an exposure value that is suitable for photographing during photographing preparation processing when the release button 12 is half-pressed. An AE detection circuit 55 and a weight coefficient calculation circuit 56 that calculates a weight coefficient used when the AE detection circuit 55 detects an exposure value are connected.

  The AF detection circuit 54 is for performing a so-called contrast AF process, calculates a focus evaluation value representing the contrast of the image from the image data digitized by the A / D 42, and sends the calculation result to the CPU 37. Send. The focus evaluation value is obtained by performing contour extraction processing with a high-pass filter or the like on a specific area of the image, for example, image data of the central portion of the shooting angle of view, and extracting the contour signal and the central portion of the image data. It is obtained by integrating the luminance value. Note that the larger the focus evaluation value is, the more high-frequency components are in the portion, and the portion is in focus. The CPU 37 acquires focus evaluation values at a plurality of positions while moving the focus lens 32 by a predetermined amount, and performs AF processing by moving the focus lens 32 to a position where the focus evaluation value is the highest.

  The AE detection circuit 55 includes an image dividing unit (dividing unit) 55a, a luminance calculating unit (luminance calculating unit) 55b, and an exposure calculating unit (exposure calculating unit) 55c. For example, as shown in FIG. 4, the image dividing unit 55 a divides the imaging screen 60 represented by the image data into a total of 64 small regions 62 of 8 columns and 8 columns. For convenience of explanation, numbers 1 to 64 are assigned to the small areas 62 in FIG. In this example, the imaging screen 60 is divided into 64 small areas 62, but the number of small areas 62 is not limited to 64. In addition, a method for dividing the small region 62 may be a known method, for example, using a gate circuit.

  The luminance calculation unit 55b calculates the subject integrated value for each small region 62 by calculating the average integrated value of the imaging signals for each small region 62. The AE detection circuit 55 that has obtained the subject brightness value for each small region 62 by the brightness computation unit 55 b transmits the obtained subject brightness value to the weight coefficient computation circuit 56.

  The weighting coefficient calculation circuit 56 includes a maximum value detection unit 56a, a difference calculation unit 56b, a function calculation unit 56c, and a center weight processing unit 56d. The weighting factor calculation circuit 56 that has received each subject luminance value from the AE detection circuit 55 inputs each received subject luminance value to the maximum value detection unit 56a. The maximum value detection unit 56a, to which each subject brightness value is input, detects the maximum subject brightness value from each small region 62 by the procedure shown in the flowchart of FIG.

  The maximum value detector 56a first sets 0 as the initial maximum value. For example, the maximum value may be set in the SDRAM 45, or may be set in a dedicated memory in the maximum value detection unit 56a. The maximum value detection unit 56a that sets the initial maximum value sets an arbitrary small region 62, for example, the small region 62 numbered 1 in FIG. 4 as the comparison region. The maximum value detection unit 56a that sets the comparison region compares the set maximum value with the subject luminance value of the comparison region, and when the subject luminance value of the comparison region is larger, sets the subject luminance value as a new maximum value. set. The maximum value detection unit 56a compares the small areas 62 from No. 1 to No. 64, and detects the maximum value of the subject luminance value by updating the smaller area 62.

  The difference calculation unit 56b subtracts the subject luminance value of each small region 62 from the maximum value detected by the maximum value detection unit 56a, and calculates a difference from the maximum value for each small region 62. This difference value increases as the subject brightness value is lower, that is, the darker, and represents a dark small area 62 in the imaging screen 60.

  The function calculation unit 56c inputs the difference value of each small region 62 calculated by the difference calculation unit 56b to the correction function, and obtains the output result. FIG. 6 shows an example of the correction function. The correction function RF in FIG. 6 draws a curve that rises to the right and bulges in the upper right portion, and outputs a larger portion of the input value, that is, a dark portion in the imaging screen 60. Thereby, it is possible to obtain a weighting coefficient in which dark portions are more emphasized. Further, the correction function RF has only a range of input values from 0 to 180. For this reason, before inputting each difference value to the correction function RF, the function calculation unit 56c performs normalization so that the maximum value of each difference value becomes 180, for example, by proportional calculation. By normalizing in this way, each difference value can be accurately applied to the correction function RF. Note that the curvature of the correction function RF and the range of the input value and the output value may be appropriately determined depending on the degree of correction. The correction function RF is stored in advance in, for example, the EEPROM 53, and is read out to the function calculation unit 56c as necessary.

  In consideration of the fact that the main subject often comes near the center of the imaging screen 60, the center emphasis processing unit 56d (for example, the small regions 62 of No. 28, 29, 36, and 37 in FIG. 4). The center-weighted photometry is performed to increase the weighting coefficient. FIG. 7 shows an example of weighting factors used in center-weighted metering. In FIG. 7, the numbers written in each area indicate the weighting coefficient. The center emphasis processing unit 56d multiplies the output value calculated for each small region 62 by the function calculation unit 56c by the center emphasis weighting coefficient shown in FIG. As a result, it is possible to obtain a weighting factor that emphasizes the dark part in the imaging screen 60 and the central part where the main subject is highly likely to come. The center-weighted weighting factor is stored in advance in the EEPROM 53, for example, and is read by the center-weighted processing unit 56d as necessary. The weighting factor calculation circuit 56 outputs the multiplication result calculated by the center emphasis processing unit 56d to the AE detection circuit 55 as a final weighting factor for each small region 62.

  The AE detection circuit 55 that has received the weighting factor from the weighting factor calculation circuit 56 exposes the received weighting factor for each small region 62 and the subject luminance value for each small region 62 initially calculated by the luminance calculation unit 55b. It inputs into the calculating part 55c. The exposure calculation unit 55c sets the exposure value to E, the subject brightness value for each small region 62 to Di (i = 1, 2,... N), and the weighting factor for each small region 62 to Wi (i = 1, 2, .., N), the exposure value E is calculated by a weighted average according to the following equation (1). However, in this example, since the number of the small regions 62 is 64, n = 64.

  The AE detection circuit 55 that has calculated the exposure value E transmits the exposure value E to the CPU 37. Based on the exposure value E transmitted from the AE detection circuit 55, the CPU 37, for example, determines an appropriate aperture value, shutter speed, etc. from a program diagram stored in advance in the EEPROM 53, etc. Control the behavior.

  Next, the operation of the digital camera 2 configured as described above will be described with reference to the flowchart shown in FIG. 8, taking the shooting scene shown in FIG. 9 as an example. Note that the shooting scene of FIG. 9 shows a scene in which the person as the main subject is dark and the background is bright due to backlight. The digital camera 2 performs shooting preparation processing including AF processing and AE processing in response to a half-press operation of the release button 12. When performing the AE process, the CPU 37 transmits the image data output from the A / D 42 to the AE detection circuit 55.

  The image data transmitted to the AE detection circuit 55 is input to the image dividing unit 55a and divided into 64 small areas 62 (see FIG. 4). The image data divided into the small areas 62 is sent to the luminance calculation unit 55b. The luminance calculation unit 55b calculates the subject luminance value of each small region 62. FIG. 10 shows a calculation result of each subject luminance value corresponding to the shooting scene of FIG. In FIG. 10, the numerical value in each small area 62 represents the subject brightness value (unit is EV) of each small area 62. From FIG. 10, the subject brightness value of the small area 62 near No. 1 to 8 corresponding to the background portion is high, and the subject brightness value of the small area 62 near No. 20, 21, 28, and 29 corresponding to the person portion is low. I understand that.

  The AE detection circuit 55 that has calculated the subject luminance value of each small area 62 transmits the calculated subject luminance value to the weighting factor calculation circuit 56 to calculate a weighting factor for obtaining an exposure value. Each subject luminance value transmitted to the weighting coefficient calculation circuit 56 is input to the maximum value detection unit 56a. As described above, the maximum value detection unit 56a compares the subject luminance values of the small areas 62 from No. 1 to No. 64, and detects the maximum value of the subject luminance value by updating to the larger one. (See FIG. 5). In FIG. 10, 16.45 EV of the fourth small area 62 is detected as the maximum value. The maximum value detection unit 56a that has detected the maximum value of the subject luminance value inputs the detected maximum value 16.45EV and the subject luminance value of each small region 62 to the difference calculation unit 56b.

  The difference calculation unit 56b subtracts the subject luminance value of each small area 62 from the maximum value 16.45EV, and calculates a difference from the maximum value for each small area 62. FIG. 11 shows the calculation result of the difference value. In FIG. 11, in order to simplify the description by eliminating the decimal point, each difference value is multiplied by 100 after subtracting the subject luminance value of each small area 62 from the maximum value 16.45 EV. In FIG. 11, the fourth small area 62 having the maximum subject luminance value is 0, and it can be seen that the numerical value of the small area 62 (for example, No. 28) having a low subject luminance value corresponding to the person portion is high. . As a result, when the final weighting factor is calculated, the weighting factor of the portion with the low subject luminance value (dark portion) is calculated to be large. The difference calculation part 56b which calculated the difference value of each small area | region 62 inputs each calculated difference value into the function calculation part 56c.

  The function calculation unit 56c normalizes each difference value so that the maximum value becomes 180 in order to input each difference value to the correction function RF (see FIG. 6). In FIG. 11, it can be seen that 650 of the 28th small region 62 is the maximum difference value. The function calculation unit 56c normalizes each difference value so that the 28th small region 62 becomes 180 as shown in FIG. The normalized function calculation unit 56c inputs each difference value after normalization to the correction function RF, and acquires an output value corresponding to the correction function RF. FIG. 13 shows the result of each acquired output value. The function calculation unit 56c that has obtained each output value inputs the obtained output value to the center emphasis processing unit 56d.

  The center emphasis processing unit 56d multiplies each output value of each small region 62 input from the function calculation unit 56c by the center emphasis weighting factor (see FIG. 7), and obtains the final weighting factor of each subregion 62. calculate. FIG. 14 shows the result of multiplying the weighting factor of the center weight. By calculating the weighting coefficient for each small area 62 as described above, weights that place importance on the dark part in the imaging screen 60 and the central part in the imaging screen 60 where the main subject (such as a person) is likely to come. A coefficient can be obtained. The weighting factor calculation circuit 56 that has calculated each weighting factor transmits the calculated weighting factor to the AE detection circuit 55.

  Each weighting coefficient transmitted to the AE detection circuit 55 is input to the exposure calculation unit 55c. Receiving each weighting coefficient, the exposure calculation unit 55c calculates an exposure value corresponding to the shooting scene shown in FIG. The CPU 37 determines a shutter speed, an aperture value, and the like based on the calculated exposure value. Table 1 below shows exposure values calculated using the weighting factors shown in FIG. 14 (hereinafter referred to as “weighting factors emphasizing low luminance”) and exposure values calculated using only the centering weighting factors. .

  As shown in Table 1, it can be seen that the exposure value calculated using the low-luminance weighting factor is about 1 EV lower than the exposure value calculated using only the center-weighting weighting factor. As a result, the CPU 37 shoots the subject brighter by 1 EV by lowering the shutter speed by one step or reducing the aperture value by one step as compared with the case of only the weighting factor of the center weight. In this way, by using the weighting factor emphasizing low luminance, the dark portion in the imaging screen is emphasized, and the subject is photographed brighter than the case of only the weighting factor of the center emphasis. Even if shooting is performed in a backlight scene where the contrast between the main subject and the background is extremely large, it is possible to prevent the person who is the main subject from being underexposed.

  In the above embodiment, the exposure value is always calculated using a weighting factor emphasizing low luminance. However, as shown in the flowchart of FIG. You may make it use properly. The AE detection circuit 55 performs the division of the imaging screen 60 by the image dividing unit 55a and the calculation of the subject luminance value of each small area 62 by the luminance calculation unit 55b, and then the entire imaging screen 60 based on each subject luminance value. The average luminance value is calculated. For example, the average luminance value may be calculated by setting all the weighting coefficients in the above equation (1) to 1.

  The AE detection circuit 55 that has calculated the average luminance value determines whether or not the average luminance value is 12 EV or more. The AE detection circuit 55 that has determined that the average luminance value is equal to or greater than 12 EV transmits each subject luminance value calculated by the luminance calculation unit 55b to the weight coefficient calculation circuit 56 in the same manner as in the above embodiment, and weights that emphasize low luminance. Let the coefficient be calculated. On the other hand, the AE detection circuit 55 that has determined that the average luminance value is 12 EV or less inputs each subject luminance value to the exposure calculation unit 55c, and calculates the exposure value using only the center-weighted weighting factor.

  If a weighting factor that emphasizes low luminance is always used as in the above-described embodiment, underexposure of the main subject can be suppressed in shooting scenes such as backlighting, but it is not possible to perform main shooting as in night spotlight shooting. If the subject is brighter than the background, the main subject may be overexposed. Therefore, in this example, when the average luminance value is 12 EV or more, it is determined that the scene is a shooting scene in which a high-luminance object such as backlight or light is reflected. Only in this case, the weighting factor emphasizing low luminance is used. I tried to do it. As a result, underexposure of the main subject in a shooting scene such as backlighting can be suppressed, and a weighting factor emphasizing low luminance can be prevented from adversely affecting other shooting scenes. In this example, the threshold value of the average luminance value is set to 12 EV. However, the threshold value is not limited to this and may be arbitrarily set in consideration of the dynamic range of the CCD 38 and the like.

  In the above embodiment, an example in which underexposure of a main subject in a shooting scene such as backlighting is suppressed has been shown. However, for example, the digital camera 2 is configured as shown in FIG. The overexposure may be suppressed. In addition, about the same thing as the said embodiment on a function and a structure, the same code is attached and detailed description is abbreviate | omitted.

  The weighting factor calculation circuit 70 includes a minimum value detection unit 70a, a difference calculation unit 70b, a function calculation unit 70c, and a center weight processing unit 70d. When the subject brightness value for each small region 62 is transmitted from the AE detection circuit 55, the weight coefficient calculation circuit 70 inputs each subject brightness value to the minimum value detection unit 70a. The minimum value detection unit 70a, to which each subject brightness value is input, detects the minimum subject brightness value from each small region 62 by the procedure shown in the flowchart of FIG.

  The minimum value detector 70a first sets 99.99 as the initial minimum value. The minimum value may be set in the SDRAM 45, for example, or may be set in a dedicated memory in the minimum value detection unit 70a. The initial minimum value is not limited to 99.99, and a sufficiently large value that is impossible as a luminance value may be set. The minimum value detection unit 70a that sets the initial minimum value sets an arbitrary small region 62, for example, the small region 62 numbered 1 in FIG. 4 as the comparison region. The maximum value detection unit 70a that sets the comparison region compares the set minimum value with the subject luminance value of the comparison region, and when the subject luminance value of the comparison region is smaller, sets the subject luminance value as a new minimum value. set. The minimum value detection unit 70a compares the small areas 62 from No. 1 to No. 64, and detects the minimum value of the subject luminance value so as to update the smaller area.

  The difference calculation unit 70 b subtracts the minimum value detected by the minimum value detection unit 70 a from the subject luminance value of each small region 62, and calculates a difference from the minimum value for each small region 62. This difference value increases as the subject brightness value is higher, that is, the brighter, and represents a bright small area 62 in the imaging screen 60.

  The function calculation unit 70c inputs the difference value of each small region 62 calculated by the difference calculation unit 70b, for example, to the correction function RF shown in FIG. 6, and obtains the output result. The correction function RF of FIG. 6 draws a curve that rises to the right and the upper right part swells, and outputs a larger input value, that is, a bright part in the imaging screen 60. Thereby, it is possible to obtain a weighting factor that emphasizes brighter portions. Similarly to the above-described embodiment, the function calculation unit 70c performs normalization so that the maximum value of each difference value is 180 before inputting each difference value to the correction function RF.

  The center emphasis processing unit 70d multiplies the output value calculated for each small region 62 by the function calculation unit 70c by the center emphasis weighting coefficient shown in FIG. As a result, it is possible to obtain a weighting factor that places importance on the bright part in the imaging screen 60 and the central part where the main subject is highly likely to come. The weighting factor calculation circuit 70 outputs the multiplication result calculated by the center emphasis processing unit 70d to the AE detection circuit 55 as a final weighting factor for each small region 62.

  Next, the operation of the digital camera 2 having the configuration shown in FIG. 16 will be described with reference to the flowchart shown in FIG. 18, taking the shooting scene shown in FIG. 19 as an example. The shooting scene of FIG. 19 shows a shooting scene in which a person who is a main subject is bright and a background is dark by applying a spotlight or the like at night. The digital camera 2 performs shooting preparation processing including AF processing and AE processing in response to a half-press operation of the release button 12. When performing the AE process, the CPU 37 transmits the image data output from the A / D 42 to the AE detection circuit 55.

  The image data transmitted to the AE detection circuit 55 is input to the image dividing unit 55a and divided into 64 small areas 62 (see FIG. 4). The image data divided into the small areas 62 is sent to the luminance calculation unit 55b. The luminance calculation unit 55b calculates the subject luminance value of each small region 62. FIG. 20 shows a calculation result of each subject luminance value corresponding to the shooting scene of FIG. In FIG. 20, the numerical value in each small area 62 represents the subject luminance value (unit: EV) of each small area 62. From FIG. 20, it can be seen that the subject luminance value of the small region 62 at both ends corresponding to the background portion is low and the subject luminance value of the small region 62 near the center corresponding to the person portion hit by the spotlight is high.

  The AE detection circuit 55 that has calculated the subject luminance value of each small area 62 transmits the calculated subject luminance value to the weighting factor calculation circuit 70 to calculate a weighting factor for obtaining an exposure value. Each subject luminance value transmitted to the weighting coefficient calculation circuit 70 is input to the minimum value detection unit 70a. As described above, the minimum value detection unit 70a compares the subject luminance values of the small areas 62 from No. 1 to No. 64, and detects the minimum value of the subject luminance value by updating the smaller one. (See FIG. 17). In FIG. 20, 3.42 EV of the 35th and 56th small regions 62 is detected as the minimum value. The minimum value detection unit 70a that detects the minimum value of the subject luminance value inputs the detected minimum value 3.42EV and the subject luminance value of each small region 62 to the difference calculation unit 70b.

  The difference calculation unit 70b subtracts the minimum value 16.45EV from each of the subject luminance values of each small area 62, and calculates a difference from the minimum value for each small area 62. FIG. 21 shows the calculation result of the difference value. In FIG. 21, in order to simplify the description by eliminating the decimal point, each difference value is multiplied by 100 after subtracting the minimum value 3.42EV from each of the subject luminance values of each small area 62. In FIG. 21, the 35th and 56th small areas 62 with the lowest subject luminance value are 0, and the numerical value of the small area 62 (for example, No. 37) having a high subject luminance value corresponding to the person portion is obtained. I understand that it is expensive. As a result, when the final weighting factor is calculated, the weighting factor of the portion with a high subject luminance value (the bright portion) is calculated to be large. The difference calculation part 70b which calculated the difference value of each small area | region 62 inputs each calculated difference value into the function calculation part 70c.

  The function calculation unit 70c performs normalization so that the maximum value of each difference value is 180 in order to input each difference value to the correction function RF (see FIG. 6). In FIG. 21, it can be seen that 569 in the 37th small area 62 is the maximum difference value. The function calculation unit 70c normalizes each difference value so that the 37th small region 62 becomes 180 as shown in FIG. The normalized function calculation unit 70c inputs each normalized difference value to the correction function RF, and acquires an output value corresponding to the correction function RF. FIG. 23 shows the results of the acquired output values. The function calculation unit 70c that has obtained each output value inputs the obtained output value to the center emphasis processing unit 70d.

  The center emphasis processing unit 70d multiplies each output value of each small region 62 input from the function calculation unit 70c by a center emphasis weighting factor (see FIG. 7), and obtains the final weighting factor of each subregion 62. calculate. FIG. 24 shows the result of multiplying the weighting factor of the center weight. By calculating the weighting coefficient for each small region 62 as described above, weights that emphasize the bright portion in the imaging screen 60 and the central portion in the imaging screen 60 where a main subject (such as a person) is likely to come. A coefficient can be obtained. The weighting factor calculation circuit 70 that has calculated each weighting factor transmits the calculated weighting factor to the AE detection circuit 55.

  Each weighting coefficient transmitted to the AE detection circuit 55 is input to the exposure calculation unit 55c. Receiving each weighting coefficient, the exposure calculation unit 55c calculates an exposure value corresponding to the shooting scene shown in FIG. The CPU 37 determines a shutter speed, an aperture value, and the like based on the calculated exposure value. Table 2 below shows exposure values calculated using the weighting factor shown in FIG. 24 (hereinafter referred to as “weighting factor emphasizing high luminance”) and exposure values calculated using only the weighting factor of the center weight. .

  As shown in Table 2, it can be seen that the exposure value calculated using the high-luminance weighting factor is about 1 EV higher than the exposure value calculated using only the center-weighting weighting factor. As a result, the CPU 37 takes the subject darker by 1 EV by increasing the shutter speed by one step or by increasing the aperture value by one step as compared with the case of using only the center-weighted weighting factor. In this way, by using a weighting factor emphasizing high luminance, the bright part in the imaging screen is emphasized, and the subject is photographed darker than the case of only the weighting factor of the center emphasis. Therefore, as shown in FIG. Even when the contrast between the main subject and the background is extremely large, such as nighttime spotlight shooting, it is possible to prevent the person who is the main subject from being overexposed.

  In the above embodiment, the exposure value is always calculated using a weighting factor emphasizing high brightness. However, as shown in the flowchart of FIG. You may make it use properly. The AE detection circuit 55 performs the division of the imaging screen 60 by the image dividing unit 55a and the calculation of the subject luminance value of each small area 62 by the luminance calculation unit 55b, and then the entire imaging screen 60 based on each subject luminance value. The average luminance value is calculated. For example, the average luminance value may be calculated by setting all the weighting coefficients in the above equation (1) to 1.

  The AE detection circuit 55 that has calculated the average luminance value determines whether or not the average luminance value is 7 EV or less. The AE detection circuit 55 that has determined that the average luminance value is 7 EV or less transmits each subject luminance value calculated by the luminance calculation unit 55b to the weighting coefficient calculation circuit 70 in the same manner as in the above embodiment, and weights that emphasize high luminance. Let the coefficient be calculated. On the other hand, the AE detection circuit 55 that has determined that the average luminance value is 7 EV or more inputs each subject luminance value to the exposure calculation unit 55c, and calculates the exposure value using only the center-weighted weight coefficient.

  If a weighting factor that emphasizes high brightness is always used as in the above embodiment, overexposure of the main subject can be suppressed in night spotlight shooting, but on the contrary, in a shooting scene such as backlighting, There is a concern that the subject may be underexposed. For this reason, in this example, when the average luminance value is 7 EV or less, it is determined that the spotlight shooting is performed at night, and the weighting factor emphasizing high luminance is used only in this case. As a result, it is possible to suppress overexposure of the main subject in spotlight shooting at night and to prevent the weighting factor emphasizing high luminance from adversely affecting other shooting scenes. In this example, the threshold value of the average luminance value is 7 EV. However, the threshold value is not limited to this and may be arbitrarily set in consideration of the dynamic range of the CCD 38.

  In each of the above embodiments, an example in which underexposure of a main subject in a shooting scene such as backlighting is suppressed and an example in which overexposure of a main subject in nighttime spotlight shooting or the like is suppressed have been described. 26 may be configured so that underexposure and overexposure of the main subject can be suppressed at the same time.

  The weighting factor calculation circuit 81 includes a maximum value detection unit 81a, a minimum value detection unit 81b, a difference calculation unit 81c, a function calculation unit 81d, and a center weight processing unit 81e. When the subject luminance value for each small area 62 is transmitted from the AE detection circuit 80, the weight coefficient calculation circuit 81 inputs each subject luminance value to the maximum value detection unit 81a and the minimum value detection unit 81b. The weighting factor emphasizing low luminance (see FIG. 8) and the weighting factor emphasizing high luminance (see FIG. 18) are respectively calculated and sent to the AE detection circuit 80.

  The AE detection circuit 80 is provided with an exposure value synthesis unit 80d in addition to the image division unit 80a, the luminance calculation unit 80b, and the exposure calculation unit 80c that are the same as those in the above embodiments. The exposure calculation unit 80c calculates an exposure value corresponding to each weighting factor based on the weighting factor emphasizing low luminance and the weighting factor emphasizing high luminance transmitted from the weighting factor calculation circuit 81. Further, the exposure calculation unit 80c reads the center-weighted weight coefficient stored in the EEPROM 53 or the like, and calculates the exposure value of only the center-weighted weight coefficient. That is, the exposure calculation unit 80c of this example calculates three exposure values using different weighting factors for one imaging screen 60 related to one AE process. The calculated exposure values are temporarily written in, for example, the SDRAM 45 or a memory provided exclusively for the AE detection circuit 80.

  The exposure value composition unit 80d obtains a composition ratio for each exposure value using a conversion function as shown in FIG. 27, and composes the three exposure values calculated by the exposure calculation unit 80c based on this composition ratio. Determine one optimal exposure value. The conversion function is provided corresponding to each exposure value, and is stored in advance in the EEPROM 53, for example. In the following, the exposure value calculated using the low-luminance weighting factor is the exposure value E1, the exposure value calculated using the high-luminance weighting factor is the exposure value E2, and the center-weighting weighting factor is used. The exposure value calculated in this way is referred to as exposure value E3, and the optimum exposure value determined by combining these values is referred to as optimum exposure value Es. A conversion function corresponding to the exposure value E1 is referred to as a conversion function CF1, a conversion function corresponding to the exposure value E2 is referred to as a conversion function CF2, and a conversion function corresponding to the exposure value E3 is referred to as a conversion function CF3.

  The exposure value synthesizing unit 80d that has obtained the respective composition ratios of the exposure values E1, E2, and E3 has the composition ratio of the exposure value E1 as R1, the composition ratio of the exposure value E2 as R2, and the composition ratio of the exposure value E3 as R3. Then, the optimum exposure value Es is calculated by the following equation (2).

  Next, the operation of the digital camera 2 configured as shown in FIG. 26 will be described with reference to the flowchart shown in FIG. The digital camera 2 performs shooting preparation processing including AF processing and AE processing in response to a half-press operation of the release button 12. When performing the AE process, the CPU 37 transmits the image data output from the A / D 42 to the AE detection circuit 80.

  The image data transmitted to the AE detection circuit 80 is input to the image dividing unit 80a and divided into 64 small regions 62 (see FIG. 4). The image data divided into the small areas 62 is sent to the luminance calculation unit 80b. The luminance calculation unit 80b calculates the subject luminance value of each small region 62.

  The AE detection circuit 80 that has calculated the subject luminance value of each small region 62 transmits the calculated subject luminance value to the weighting factor calculation circuit 81 to calculate a weighting factor for obtaining an exposure value. The weighting factor calculation circuit 81 that has received each subject luminance value calculates a weighting factor emphasizing low luminance and a weighting factor emphasizing high luminance from each subject luminance value according to the procedures shown in FIGS. 8 and 18, respectively. Are transmitted to the AE detection circuit 80.

  Each weighting factor transmitted to the AE detection circuit 80 is input to the exposure calculation unit 80c. The exposure calculation unit 80c that has received each weighting factor, based on the above equation (1), exposes an exposure value E1 that uses a weighting factor that emphasizes low luminance, an exposure value E2 that uses a weighting factor that emphasizes high luminance, and the center. The exposure value E3 using the weighting factor of importance (see FIG. 7) is calculated. Each calculated exposure value is input to the exposure value composition unit 80d.

  When the calculation of the exposure values E1, E2, and E3 by the exposure calculation unit 80c is completed, the exposure value synthesis unit 80d first calculates the average luminance value of the entire imaging screen 60 based on the subject luminance value for each small region 62. . The exposure value combining unit 80d that has calculated the average luminance value refers to the conversion functions CF1, CF2, and CF3, and determines the combined ratios R1, R2, and R3 of the exposure values E1, E2, and E3 according to the average luminance value. . For each conversion function CF1, CF2, CF3, the higher the average luminance value, the larger the combined ratio R1 of the exposure value E1, the lower the average luminance value, the larger the combined ratio R2 of the exposed value E2, and the average luminance value near the middle. Then, the composition ratio R3 of the exposure value E3 is increased.

  As described above, when the average luminance value is high, it can be determined that the shooting scene includes a high-luminance object such as backlight or light. For this reason, when the average luminance value is high, underexposure of the main subject can be suppressed by increasing the composition ratio R1 of the exposure value E1 using a weighting factor emphasizing low luminance. On the other hand, when the average luminance value is low, it can be determined that the scene is a shooting scene with a spotlight applied at night. For this reason, when the average luminance value is low, overexposure of the main subject can be suppressed by increasing the composition ratio R2 of the exposure value E2 using a weighting factor emphasizing high luminance. For the average luminance value near the middle, by increasing the composition ratio R3 of the exposure value E3 using the center-weighted weighting factor, the weighting factor emphasizing low luminance or the weighting factor emphasizing high luminance becomes the exposure of the main subject. Can be prevented from adversely affecting.

  For example, it is assumed that the calculation result of each subject luminance value by the luminance calculation unit 80b is obtained as shown in FIG. When each subject luminance value is transmitted to the weighting factor calculation circuit 81 and each weighting factor is calculated according to the procedure shown in FIG. 8 and FIG. 18, the weighting factor emphasizing low luminance is shown in FIG. As shown in FIG. When the calculated weighting factors are transmitted to the AE detection circuit 80 and the exposure values E1, E2, and E3 corresponding to the weighting factors are calculated by the exposure calculation unit 80c, the calculation results are obtained as shown in Table 3 below. It is done.

  Further, as shown in Table 3, when the average luminance value of each subject luminance in FIG. 29 is calculated using the above equation (1), 13.64 EV can be obtained. The exposure value synthesizing unit 80d refers to the respective conversion functions CF1, CF2, and CF3 and obtains the respective synthesis ratios R1, R2, and R3 according to the average luminance value. As shown in FIG. 27, when the average luminance value is 13.64 EV, the composition ratio R1 is 46, the composition ratio R2 is 0, and the composition ratio R3 is 17, respectively.

  By substituting the obtained composite ratios R1, R2, and R3 and the exposure values E1, E2, and E3 into the above equation (2), the optimal exposure value Es is calculated as 12.28 EV. That is, in the shooting scene given each subject luminance value in FIG. 29, it is possible to perform shooting without greatly removing the exposure from the main subject by determining the shutter speed, aperture value, etc. according to 12.28 EV. .

  In the above embodiment, the optimum exposure value Es is calculated based on the three exposure values E1, E2, and E3 based on the three types of weighting factors. However, the number of exposure values based on the exposure value is limited to three. Alternatively, the optimum exposure value Es may be calculated based on three or more exposure values using more exposure value calculation methods. The conversion functions CF1, CF2, and CF3 are not limited to the above, and may be arbitrarily set in consideration of various design items such as the dynamic range of the CCD 38.

  Further, in each of the above embodiments, the digital camera 2 is shown as an example of the imaging device, but the present invention is not limited to this, and can be applied to, for example, a camera-equipped mobile phone.

It is a perspective view of the front direction which shows the external appearance of a digital camera. It is a top view of the back direction which shows the external appearance of a digital camera. It is a block diagram which shows the internal structure of a digital camera schematically. It is explanatory drawing which shows an example which divides | segments an imaging screen into a some small area. It is a flowchart which shows the procedure which detects the maximum value of the subject luminance value of each small area. It is a graph which shows an example of a correction function. It is explanatory drawing which shows an example of the weighting coefficient of a center weight. It is a flowchart which shows the procedure which calculates the exposure value using the weighting factor which emphasizes low luminance. It is explanatory drawing which shows an example of the imaging | photography scene of backlight. FIG. 10 is an explanatory diagram showing subject luminance values of each small area corresponding to the shooting scene of FIG. 9. It is explanatory drawing which shows the difference from the maximum value of each to-be-photographed object luminance value. It is explanatory drawing which shows each difference value after normalization. It is explanatory drawing which shows the output value after substituting to a correction function. FIG. 10 is an explanatory diagram illustrating a weighting factor emphasizing low luminance according to the shooting scene of FIG. 9. It is a flowchart which shows the example which calculates the weighting coefficient which attaches importance to low luminance only when the average luminance value is a predetermined value or more. It is a block diagram which shows the internal structure of the digital camera at the time of suppressing the overexposure of the main subject. It is a flowchart which shows the procedure which detects the minimum value of the photographic subject luminance value of each small area. It is a flowchart which shows the procedure which calculates the exposure value using the weighting factor emphasizing high brightness. It is explanatory drawing which shows an example of the imaging | photography scene which applied the spotlight at night. It is explanatory drawing which shows the to-be-photographed object luminance value of each small area | region according to the imaging | photography scene of FIG. It is explanatory drawing which shows the difference from the minimum value of each subject luminance value. It is explanatory drawing which shows each difference value after normalization. It is explanatory drawing which shows the output value after substituting to a correction function. FIG. 20 is an explanatory diagram illustrating a weighting factor emphasizing high luminance according to the shooting scene of FIG. 19. It is a flowchart which shows the example which calculates the weighting coefficient emphasizing high luminance only when the average luminance value is a predetermined value or less. It is a block diagram which shows the internal structure of the digital camera at the time of suppressing underexposure and overexposure of the main subject. It is a graph which shows an example of each conversion function. It is a flowchart which shows the procedure which calculates the optimal exposure value Es. It is explanatory drawing which shows an example of the photographic subject luminance value of each small area | region. FIG. 30 is an explanatory diagram illustrating a weighting factor emphasizing low luminance according to the shooting scene of FIG. 29. FIG. 30 is an explanatory diagram illustrating a weighting factor emphasizing high luminance according to the shooting scene of FIG. 29.

Explanation of symbols

2 Digital Camera 10 Imaging Lens 31 Aperture 37 CPU (Exposure Control Means)
38 CCD (imaging device)
55, 80 AE detection circuit 55a, 80a Image dividing unit (dividing means)
55b, 80b Luminance calculation unit (luminance calculation means)
55c, 80c Exposure calculation unit (exposure calculation means)
56, 70, 81 Weight coefficient calculation circuit 56a, 81a Maximum value detection unit 56b, 70b, 81c Difference calculation unit 56c, 70c, 81d Function calculation unit 56d, 70d, 81e Center weight processing unit 70a, 81b Minimum value detection unit 80d Exposure Value composition part

Claims (12)

A data acquisition step for acquiring image data corresponding to the subject image from an image sensor that captures the subject image transmitted through the imaging lens, a division step for dividing the imaging screen represented by the image data into a plurality of small regions, and the small step A luminance calculation step for calculating a subject luminance value for each region, and multiplying each subject luminance value by a weighting factor set for each small region to obtain a weighted average. In the exposure value calculation method for calculating the exposure value,
An exposure value calculation method comprising a weighting coefficient calculation step for setting each calculation weighting coefficient so that the weighting is increased in the small area with the lower subject luminance value.   The weighting factor calculating step includes a step of detecting a maximum value of the subject luminance values, and a step of subtracting the subject luminance values from the maximum value to obtain a difference value from the maximum value for each small region. A step of inputting each difference value to a correction function for converting so that a larger input value portion becomes larger and obtaining an output value corresponding to the correction function, and increasing the weighting of the central portion of the imaging screen And multiplying each of the small regions by a weight factor of a center weight set in advance and each of the output values, and setting the multiplication result as the weighting factor for each calculation. The exposure value calculation method according to claim 1.   The exposure value calculation method according to claim 2, wherein each difference value is normalized to a value corresponding to an input range of the correction function before being input to the correction function. After the luminance calculation step, an average luminance value calculating step for calculating an average luminance value of each subject luminance value;
Performing a determination step of determining whether or not the average luminance value is equal to or greater than a predetermined value;
When it is determined that the average luminance value is equal to or greater than a predetermined value, the weighting coefficient calculation step is performed. When it is determined that the average luminance value is equal to or less than the predetermined value, a central portion of the imaging screen 4. The exposure value is calculated using a weighting factor of a center weight set in advance in each of the small regions so as to increase the weighting of each of the subregions as the weighting factor for each calculation. 5. The exposure value calculation method according to claim 1. A data acquisition step for acquiring image data corresponding to the subject image from an image sensor that captures the subject image transmitted through the imaging lens, a division step for dividing the imaging screen represented by the image data into a plurality of small regions, and the small step A luminance calculation step for calculating a subject luminance value for each region, and multiplying each subject luminance value by a weighting factor set for each small region to obtain a weighted average. In the exposure value calculation method for calculating the exposure value,
An exposure value calculation method comprising a weighting factor calculation step for setting each calculation weighting factor such that the weighting is increased in the small region having a higher subject luminance value.   The weighting factor calculating step includes a step of detecting a minimum value of each subject luminance value, and a step of obtaining a difference value from the minimum value for each small region by subtracting the minimum value from each subject luminance value. A step of inputting each difference value to a correction function for converting so that a larger input value portion becomes larger and obtaining an output value corresponding to the correction function, and increasing the weighting of the central portion of the imaging screen And multiplying each of the small regions by a weight factor of a center weight set in advance and each of the output values, and setting the multiplication result as the weighting factor for each calculation. The exposure value calculation method according to claim 5.   7. The exposure value calculation method according to claim 6, wherein each difference value is normalized to a value corresponding to an input range of the correction function before being input to the correction function. After the luminance calculation step, an average luminance value calculating step for calculating an average luminance value of each subject luminance value;
Performing a determination step of determining whether or not the average luminance value is equal to or greater than a predetermined value;
When it is determined that the average luminance value is equal to or less than a predetermined value, the weighting factor calculation step is performed. When it is determined that the average luminance value is equal to or greater than a predetermined value, a central portion of the imaging screen 8. The exposure value is calculated using a weighting factor of a center weight set in advance in each of the small regions so as to increase the weighting of each of the subregions as the weighting factor for each calculation. The exposure value calculation method according to claim 1. A data acquisition step for acquiring image data corresponding to the subject image from an image sensor that captures the subject image that has passed through the imaging lens, a division step for dividing the imaging screen represented by the image data into a plurality of small regions, and the small step A luminance calculation step for calculating a subject luminance value for each region, and multiplying each subject luminance value by a weighting factor set for each small region to obtain a weighted average to obtain an exposure value of the image data In the exposure value calculation method for calculating
A plurality of exposure value calculating steps for calculating a plurality of the exposure values using a plurality of weighting factors having different weights;
An average luminance value calculating step for calculating an average luminance value of each subject luminance value;
With reference to a conversion function provided for each exposure value, a combination ratio acquisition step of acquiring a combination ratio of the exposure values according to the average luminance value;
An exposure value calculation method comprising: an optimum exposure value calculation step of determining one optimum exposure value from each exposure value and each composition ratio.   The plurality of weighting factors are set such that at least the first weighting factor set so as to increase the weight in the small region with the lower subject luminance value and the weighting in the small region with the higher subject luminance value. The exposure value calculation method according to claim 9, further comprising: a set second weighting factor and a third weighting factor set such that the smaller the region in the center of the imaging screen, the higher the weighting. The first weighting coefficient detects a maximum value of each subject luminance value, subtracts each subject luminance value from the maximum value, obtains a difference value from the maximum value for each small region, and inputs an input value Each of the difference values is input to a correction function that converts the larger portion of the correction function to be larger, an output value corresponding to the correction function is obtained, and the preset third weighting factor and each output value are obtained. Set by multiplying,
The second weighting coefficient detects a minimum value of each subject luminance value, subtracts the minimum value from each subject luminance value, obtains a difference value from the minimum value for each small region, and inputs an input value Each of the difference values is input to a correction function that converts the larger portion of the correction function to be larger, an output value corresponding to the correction function is obtained, and the preset third weighting factor and each output value are obtained. The exposure value calculation method according to claim 10, wherein the exposure value calculation method is set by multiplication. An image sensor that captures a subject image that has passed through an imaging lens and outputs image data corresponding to the subject image, an aperture that adjusts the amount of light incident on the image sensor, and an imaging screen represented by the image data A dividing unit that divides the image into regions; a luminance calculating unit that calculates a subject luminance value for each of the small regions; an exposure calculating unit that calculates an exposure value of the image data based on each of the subject luminance values; In an imaging apparatus comprising exposure control means for controlling at least one of the aperture value of the aperture and the exposure time of the image sensor based on an exposure value,
12. The imaging apparatus according to claim 1, wherein the exposure calculation means calculates the exposure value using the exposure value calculation method according to any one of claims 1 to 11.

Images