JP2008182351A - Imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce halation and color saturation of an imaging device. <P>SOLUTION: A photographic area is divided into a plurality of areas, luminance values (y) are detected for the divided areas, and a tentative exposure value α is found from the detected luminance values (y) of the respective divided areas. A saturation limit value δ is added to the found tentative exposure value α to find a luminance value (saturation estimated luminance value γ) at which saturation is estimated. The found saturation estimated luminance value γ is compared with the luminance values (y) of the respective divided areas to detect the number (saturation estimated area number S) of divided areas whose luminance value (y) exceeds the saturation estimated luminance value γ. A correction quantity ε corresponding to the detected number S of saturation estimated areas is found using a function F(S). The tentative exposure value α is corrected with the found correction quantity ε to find a final exposure value β. Exposure is determined on the basis of the found final exposure value β. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an imaging apparatus, and more particularly to an imaging apparatus that corrects an exposure value obtained from a photometric result of a subject so as to prevent an image from being overexposed and color saturation.

Generally, a camera is equipped with an AE (Automatic Exposure) function so that an appropriate exposure can be automatically obtained according to the brightness of the subject. Various proposals have been made to improve the performance of the AE. For example, in Patent Document 1, the imaging region is divided into a plurality of regions, the luminance is measured in each region, and the exposure value is obtained from the measurement result, while the maximum value of the luminance measured in each region is detected, A method for correcting the exposure value according to the difference between the maximum value and the exposure value has been proposed.
JP 2001-45363 A

  However, even a camera having an AE function has a drawback in that when a scene with a large luminance difference is photographed, the exposure limit of the film or the image sensor is exceeded and whiteout or color saturation occurs.

  The present invention has been made in view of such circumstances, and an object thereof is to provide an imaging apparatus capable of reducing the occurrence of whiteout and color saturation.

  According to a first aspect of the present invention, in order to achieve the above object, in a photographing apparatus that determines an exposure based on an exposure value obtained from a photometric result of a subject, a luminance value that is expected to be saturated based on the exposure value. Is calculated by a saturation predicted brightness value calculating means, a photographing area is divided into a plurality of areas, a brightness value detecting means for detecting a brightness value for each divided area, and the brightness value detecting means Saturation prediction area number detection means for detecting the number of divided areas whose luminance value exceeds the saturation prediction luminance value as the saturation prediction area number, and correction according to the saturation prediction area number using a predetermined function or table There is provided an imaging apparatus comprising: a correction amount acquisition unit that acquires an amount; and an exposure value correction unit that corrects the exposure value with the correction amount acquired by the correction amount acquisition unit.

  According to the first aspect of the present invention, the imaging region is divided into a plurality of regions, the luminance value is detected for each divided region, and the number of the divided regions in which the detected luminance value exceeds the saturation expected luminance value is saturated. It is detected as the expected number of areas. Then, the exposure value is corrected according to the detected number of expected saturation areas. As a result, even in a scene with a large luminance difference, it is possible to shoot while suppressing the occurrence of whiteout.

  In order to achieve the above object, the invention according to claim 2 is a maximum luminance value detecting means for detecting a maximum luminance value as a maximum luminance value among the luminance values detected for each divided region by the luminance value detecting means. And a correction for correcting or changing the function or the table so that the difference between the maximum luminance value detected by the maximum luminance value detecting means and the saturation expected luminance value is the maximum value of the correction amount. And a photographing device according to claim 1.

  According to the invention of claim 2, the difference between the maximum luminance value and the saturation expected luminance value is obtained, and the function or table is corrected or changed so that the obtained difference becomes the maximum value of the correction amount. Thereby, it is possible to prevent the exposure value from being corrected more than necessary, and to more effectively prevent the occurrence of whiteout.

  The invention according to claim 3 is characterized in that, in order to achieve the object, an exposure value is obtained based on a luminance value detected for each divided region by the luminance value detecting means. A photographing apparatus is provided.

  According to the invention of claim 3, the exposure value is obtained based on the luminance value detected for each divided region. Thereby, the exposure value and its correction amount can be obtained efficiently.

  According to a fourth aspect of the present invention, in order to achieve the above object, in a photographing apparatus that determines exposure based on an exposure value obtained from a photometric result of a subject, a luminance value that is expected to be saturated based on the exposure value. Is calculated as a saturation expected luminance value, a photographed area is divided into a plurality of areas, and a metering means for measuring each divided area for each of R, G, and B, and a light metering by the metering means. A saturated expected area number detecting means for detecting the number of divided areas in which at least one of the photometric values for each of R, G, and B exceeds the saturation expected luminance value as the predicted saturation area number, and a predetermined function or table are used. Correction amount acquisition means for acquiring a correction amount according to the number of expected saturation areas, and exposure value correction means for correcting the exposure value with the correction amount acquired by the correction amount acquisition means. Shooting To provide a location.

  According to the fourth aspect of the present invention, the photographing area is divided into a plurality of areas, and each divided area is measured for each of R, G, and B, and at least one of the photometric values for each of R, G, and B is measured. The number of divided areas exceeding the saturation expected luminance value is detected as the number of saturation expected areas. Then, the exposure value is corrected according to the detected number of expected saturation areas. As a result, even a scene with a large luminance difference can be photographed while suppressing occurrence of whiteout and color saturation.

  In order to achieve the above object, the invention according to claim 5 detects the maximum photometric value as the maximum photometric value among the photometric values for each of R, G, and B measured by the photometric detection means for each divided region. And calculating the difference between the maximum photometric value detected by the maximum photometric value detection unit and the saturation expected luminance value, and the function or table so that the calculated difference becomes the maximum value of the correction amount. The imaging apparatus according to claim 4, further comprising: a correcting unit that corrects or changes the information.

  According to the fifth aspect of the invention, the difference between the maximum photometric value and the saturation expected luminance value is obtained, and the function or table is corrected or changed so that the obtained difference becomes the maximum value of the correction amount. As a result, it is possible to prevent the exposure value from being corrected more than necessary, and to more effectively prevent whiteout and color saturation.

  The invention according to claim 6 is characterized in that, in order to achieve the object, an exposure value is obtained based on a photometric value for each of R, G, and B that is measured for each divided region by the photometric means. An imaging apparatus according to 4 or 5 is provided.

  According to the invention which concerns on Claim 6, an exposure value is calculated | required based on the photometric value for every R, G, and B photometrically measured for every division area. Thereby, the exposure value and its correction amount can be obtained efficiently.

  With the photographing apparatus according to the present invention, it is possible to reduce the occurrence of whiteout and color saturation.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, the best mode for carrying out an imaging apparatus according to the invention will be described with reference to the accompanying drawings.

  FIG. 1 is a block diagram showing an electrical configuration of a first embodiment of a digital camera to which the present invention is applied.

  As shown in the figure, the digital camera 10 of the present embodiment includes a photographing lens 12, an image sensor 14, an analog signal processing unit 16, an A / D converter 18, an image input controller 20, a digital signal processing unit 22, and a compression. / Extension processing unit 24, display control unit 26, liquid crystal monitor 28, recording control unit 30, storage medium 32, AF detection unit 34, AE / AWB detection unit 36, luminance calculation unit 38, CPU 40, ROM 42, RAM 44, flash memory 46 , VRAM 48, operation unit 50, comparison / counting processing unit 52, and the like.

  Each unit operates under the control of the CPU 40, and the CPU 40 controls each unit of the digital camera 10 by executing a predetermined control program based on an input from the operation unit 50.

  In addition to the control program executed by the CPU 40, various data necessary for control are recorded in the ROM 42. The CPU 40 controls each unit of the digital camera 10 by reading the control program recorded in the ROM 42 into the RAM 44 and sequentially executing the program.

  The RAM 44 is used as a program execution processing area, a temporary storage area for image data, and various work areas.

  The flash memory 46 is used as a recording area for various setting information such as user setting information, and the VRAM 48 is used as a recording area dedicated for display image data.

  The operation unit 50 includes general camera operation means such as a shutter button, zoom lever, menu button, execution button, cancel button, mode switching dial, and power button, and outputs a signal corresponding to the operation to the CPU 40.

  The photographing lens 12 is composed of an AF lens having a zoom function, and includes a focus lens 12F, a zoom lens 12Z, and a diaphragm 12I.

  The focus lens 12F is driven by the focus motor 60F and moves back and forth on the optical axis of the photographing lens 12. The CPU 40 controls the movement of the focus lens 12F by controlling the drive of the focus motor 60F via the focus motor driver 62F, and performs the focusing of the photographing lens 12.

  The zoom lens 12Z is driven by the zoom motor 60Z and moves back and forth on the optical axis of the photographing lens 12. The CPU 40 controls the movement of the zoom lens 12Z by controlling the drive of the zoom motor 60Z via the zoom motor driver 62Z, and zooms the photographing lens 12.

  The diaphragm 12I is constituted by an iris diaphragm, for example, and is driven by an iris motor 60I to operate. The CPU 40 controls the operation of the aperture 12I (controls the aperture amount) and controls the exposure amount to the image sensor 14 by controlling the driving of the iris motor 60I via the iris motor driver 62I.

  The image sensor 14 is arranged at the rear stage of the photographing lens 12 and receives subject light transmitted through the photographing lens 12. In the digital camera 10 of the present embodiment, a color CCD image sensor (CCD) 14 is used as an image sensor. As is well known, the CCD 14 has a light receiving surface on which a large number of light receiving elements are arranged in a matrix. The subject light transmitted through the photographic lens 12 is imaged on the light receiving surface of the CCD 14 and converted into an electric signal by each light receiving element.

  The CCD 14 outputs the charges accumulated in each pixel as a serial image signal line by line in synchronization with the vertical transfer clock and horizontal transfer clock supplied from the CCD driver 64. The CPU 40 controls the CCD driver 64 to control the driving of the CCD 14.

  The charge accumulation time (exposure time) of each pixel is determined by an electronic shutter drive signal given from the CCD driver 64. The CPU 40 instructs the CCD driver 64 about the charge accumulation time.

  The output of the image signal is started when the digital camera 10 is set to the shooting mode. That is, when the digital camera 10 is set to the photographing mode, output of an image signal is started to display a through image on the liquid crystal monitor 28. The output of the image signal for the through image is temporarily stopped when the instruction for the main photographing is given, and is started again when the main photographing is finished.

  The image signal output from the CCD 14 is an analog signal, and this analog image signal is taken into the analog signal processing unit 16.

  The analog signal processing unit 16 includes a correlated double sampling circuit (CDS) and an automatic gain control circuit (AGC). The CDS removes noise contained in the image signal, and the AGC amplifies the noise-removed image signal with a predetermined gain. The analog image signal subjected to the required signal processing by the analog signal processing unit 16 is taken into the A / D converter 18.

  The A / D converter 18 converts the captured analog image signal into a digital image signal having a gradation width of a predetermined bit. This image signal is so-called RAW data, and has a gradation value indicating the density of R, G, and B for each pixel.

  The image input controller 20 has a built-in line buffer having a predetermined capacity, and stores the image signal for one frame output from the A / D converter 18. The image signal for one frame accumulated in the image input controller 20 is stored in the RAM 44 via the bus 54.

  In addition to the CPU 40, ROM 42, RAM 44, flash memory 46, VRAM 48, and image input controller 20, the bus 54 includes a digital signal processing unit 22, compression / decompression processing unit 24, display control unit 26, recording control unit 30, and AF detection. A unit 34, an AE / AWB detection unit 36, a comparison / coefficient processing unit 52, and the like are connected to each other, and these can exchange information with each other via a bus 54.

  The image signal for one frame stored in the RAM 44 is taken into the digital signal processing unit 22 in dot order (pixel order).

  The digital signal processing unit 22 performs predetermined signal processing on the image signals of R, G, and B colors captured in a dot-sequential manner, and outputs an image signal (Y / C) composed of a luminance signal Y and color difference signals Cr and Cb. Signal).

  FIG. 2 is a block diagram showing a schematic configuration of the digital signal processing unit 22.

  As shown in the figure, the digital signal processing unit 22 includes a white balance gain calculation circuit 22a, an offset correction circuit 22b, a gain correction circuit 22c, a gradation correction circuit 22d, an RGB interpolation calculation circuit 22e, an RGB / YC conversion circuit 22f, It includes a noise filter 22g, a contour correction circuit 22h, a color difference matrix circuit 22i, a light source type determination circuit 22j, and the like.

  In order to perform white balance adjustment, the white balance gain calculation circuit 22a takes in an integrated value calculated by an AE / AWB detection unit 36, which will be described later, and calculates a gain value for white balance adjustment.

  The offset correction circuit 22b performs predetermined offset processing on the image signals of R, G, and B colors that are fetched dot-sequentially from the RAM 44 so that black is expressed when a black subject is photographed. That is, a preset offset value is subtracted from the image signals of R, G, and B colors.

  The gain correction circuit 22c takes the image signal subjected to the offset process in a dot-sequential manner, and performs white balance adjustment using the gain value calculated by the white balance gain calculation circuit 22a.

  The gradation correction circuit 22d takes in the image signal adjusted in white balance dot-sequentially and performs a predetermined gradation conversion process. That is, when the image data is output to the monitor, a deviation occurs between the gradation value input to the monitor and the gradation value output from the monitor. Therefore, in order to correct this deviation, an image obtained by photographing is obtained. A predetermined gradation conversion process (so-called gamma correction) is performed on the signal.

  The RGB interpolation calculation circuit 22e interpolates R, G, and B color signals that have been subjected to gradation conversion processing to obtain R, G, and B3 color signals at each pixel position. That is, in the case of a single-plate image sensor, only one color signal of R, G, and B is output from each pixel, so that a color that is not output is obtained from the color signals of surrounding pixels by a complementary operation. For example, in a pixel that outputs R, the level of G and B color signals at this pixel position is determined by interpolation from the G and B signals of surrounding pixels.

  Note that the RGB complementary calculation is unique to the single-plate image sensor, and thus is not necessary when a three-plate image sensor is used.

  The RGB / YC conversion circuit 22f generates a luminance signal Y and color difference signals Cr and Cb from the R, G, and B signals after the RGB interpolation calculation.

  The noise filter 22g performs noise reduction processing on the luminance signal Y and the color difference signals Cr and Cb generated by the RGB / YC conversion circuit 22f. The luminance signal Y and the color difference signals Cr and Cb subjected to noise reduction processing by the noise filter 22g are taken into the contour correction circuit 22h and the color difference matrix circuit 22i, respectively.

  The color difference matrix circuit 22i performs color tone correction by multiplying the color difference signals Cr and Cb by a predetermined color difference matrix (C-MTX). That is, the color difference matrix circuit 22i is provided with a plurality of types of color difference matrices corresponding to the light sources, and the color difference matrix to be used is switched according to the light source type obtained by the light source type determination circuit 22j. The inputted color difference signals Cr and Cb are multiplied to correct the color tone of the color difference signals Cr and Cb.

  The light source type determination circuit 22j takes the integrated value calculated by the AE / AWB detection unit 36, determines the light source type, and outputs a color difference matrix selection signal to the color difference matrix circuit 22i.

  The contour correction circuit 22h performs a predetermined contour correction process on the luminance signal Y.

  As described above, the digital signal processing unit 22 performs predetermined signal processing on the R, G, and B image signals captured in a dot-sequential manner, and generates an image signal (Y that includes the luminance signal Y and the color difference signals Cr and Cb). / C signal).

  The AF detection unit 34 takes in R, G, and B image signals stored in the RAM 44 via the image input controller 20 in accordance with a command from the CPU 40, and calculates a focus evaluation value necessary for AF (Automatic Focus) control. The AF detection unit 34 includes a high-pass filter that passes only a high-frequency component of the G signal, an absolute value processing unit, a focus region extraction unit that extracts a signal within a predetermined focus region set on the screen, An integration unit for integrating the absolute value data is included, and the absolute value data in the focus area integrated by the integration unit is output to the CPU 40 as a focus evaluation value. During the AF control, the CPU 40 searches for a position where the focus evaluation value output from the AF detection unit 34 is maximized, and moves the focus lens 12F of the photographing lens 12 to that position, thereby focusing on the main subject. I do.

  The AE / AWB detection unit 36 takes in R, G, and B image signals stored in the RAM 44 via the image input controller 20 in accordance with a command from the CPU 40, and performs integration necessary for AE control and AWB (Automatic White Balance) control. Calculate the value. That is, the AE / AWB detection unit 36 divides the imaging region (one screen) into a plurality of regions, and calculates an integrated value of image signals for each of R, G, and B for each divided region.

  In the digital camera according to the present embodiment, one screen is equally divided into 64 (8 × 8) regions, and the integrated value of image signals for each of R, G, and B is calculated for each divided region. The calculated integrated value information for each R, G, B in each divided area is stored in the RAM 44.

  During the AWB control, the CPU 40 determines the integrated value of the image signals for each of R, G, and B in each divided area calculated by the AE / AWB detection unit 36, the white balance gain calculation circuit 22a of the digital signal processing unit 22, and the light source type determination. Add to circuit 22j. The white balance gain calculation circuit 22a calculates a gain value for white balance adjustment based on the integrated value of the image signals for each of R, G, and B in each divided area calculated by the AE / AWB detection unit. The light source type determination circuit 22j detects the light source type based on the integrated value of the image signals for each of R, G, and B in each divided region calculated by the AE / AWB detector 36.

  In addition, during the AE control, the CPU 40 adds the integrated value of the image signal for each of R, G, and B in each divided area calculated by the AE / AWB detection unit 36 to the luminance calculation unit 38. As shown in FIG. 3, the luminance calculation unit 38 obtains the integrated value of the image signal for each of R, G, and B in each divided area calculated by the AE / AWB detection unit 36 and when the image signal is obtained. The photometric values r, g, and b for each of R, G, and B in each divided region are calculated based on the information on the imaging conditions (aperture value, shutter speed, and imaging sensitivity). Then, based on the obtained photometric values r, g, b for each R, G, B in each divided area and the gain values WBr, WBg, WBb for white balance adjustment, the luminance value in each divided area from the following equation: y is calculated.

[Equation 1]
y = log ₂ (0.299 * 2 ^{WBr * r} + 0.587 * 2 ^{WBg * g} + 0.114 * 2 ^{WBb * b} )
Information on the calculated luminance value y in each divided area is stored in the RAM 44.

  The CPU 40 obtains a temporary exposure value (Ev value) α from the calculated luminance value y in each divided area. In addition, the calculation method of temporary exposure value (alpha) is not specifically limited, It can calculate using a well-known method. For example, in the method of calculating the average of the luminance values of the entire screen and using this as a temporary exposure value (so-called average metering method) or the average metering method, weighting the area near the center of the screen Method (so-called center forward point metering method), a method of calculating the average of brightness values in a very narrow area of an image, and using this as a temporary exposure value (so-called spot metering method), dividing the screen into a plurality of regions, Various methods are used such as a method (so-called divided photometry method) in which pattern recognition processing is performed to predict the most important region, the average of luminance values in the region is obtained, and this is used as a temporary exposure value. be able to.

  In the digital camera of the present embodiment, it is assumed that the user can select these photometry methods, and a temporary exposure value is calculated under the selected photometry method.

  The CPU 40 performs exposure correction as necessary for the calculated temporary exposure value α, and performs exposure setting based on the finally obtained exposure value (final exposure value) β. That is, the aperture value and shutter speed are determined from the final exposure value β according to a predetermined program diagram.

  In addition, the CPU 40 calculates a predicted saturation luminance value γ from the calculated temporary exposure value α and outputs it to the comparison / count processing unit 52.

  Here, the saturation expected luminance value γ is obtained as a value obtained by adding a predetermined saturation limit value δ to the calculated temporary exposure value α.

  Films and image sensors (CCD / CMOS image sensors, etc.) have a limit width that can identify gradations called latitude / dynamic range. If the luminance exceeds the limit where the gradation can be identified, it results in overexposure or blackout. The limit on the highlight side is generally 3 Ev for a film and about 2 Ev for an image sensor such as a CCD / CMOS for proper exposure.

  Therefore, in the digital camera of the present embodiment, the saturation limit value δ is defined as 2Ev, and a value obtained by adding the saturation limit value δ to the temporary exposure value α is calculated as the saturation expected luminance value γ.

  The information on the saturation limit value δ is assumed to be stored in the ROM 42 in advance, and the CPU 40 reads the information on the saturation limit value δ from the ROM 42 and calculates the saturation expected luminance value γ. Then, the obtained saturation predicted luminance value γ is output to the comparison / count processing unit 52. The comparison / counting processing unit 52 calculates a correction amount ε to be applied to the temporary exposure value α based on the obtained predicted saturation luminance value γ and information on the luminance value y in each divided region. A method of calculating the correction amount ε in the comparison / counting processing unit 52 will be described in detail later.

  In accordance with a compression command from the CPU 40, the compression / expansion processing unit 24 performs compression processing in a predetermined format (for example, JPEG) on an image signal (Y / C signal) composed of the input luminance signal Y and color difference signals Cr and Cb. To generate compressed image data. Further, in accordance with a decompression command from the CPU 40, the input compressed image data is subjected to a decompression process in a predetermined format to generate uncompressed image data.

  The display control unit 26 controls display on the liquid crystal monitor 28 in accordance with a command from the CPU 40. That is, in accordance with a command from the CPU 40, the image signals sequentially input from the VRAM 48 are converted into video signals (for example, NTSC signal, PAL signal, SCAM signal) for display on the liquid crystal monitor 28, and output to the liquid crystal monitor 28. Further, if necessary, signals such as characters, figures and symbols to be displayed on the liquid crystal monitor 28 are mixed with the image signal so that predetermined characters, figures and symbols are displayed on the liquid crystal monitor 28.

  The recording control unit 30 controls reading / writing of data with respect to the storage medium 32 in accordance with a command from the CPU 40. The storage medium 32 may be detachable from the camera body such as a memory card, or may be built into the camera body. In the case of detachable, a card slot is provided in the camera body, and the card slot is used by being loaded.

  As described above, the comparison / count processing unit 52 calculates the provisional exposure value α based on the saturation expected luminance value γ calculated by the CPU 40 and the luminance value y in each divided region calculated by the luminance calculation unit 38. A correction amount ε to be applied to is calculated. That is, as shown in FIG. 4, the luminance value y in each divided region is compared with the saturation predicted luminance value γ, and the number of divided regions in which the luminance value y exceeds the saturation predicted luminance value γ is determined as the number of saturated predicted regions S. And a correction amount ε corresponding to the obtained saturation expected area number S is calculated. This correction amount ε is calculated using a function F (S) in which the correction amount ε is defined according to the number S of expected saturation regions.

  For example, it is assumed that a subject (photographing scene) as shown in FIG. 5 is photographed and a luminance value y as shown in FIG. 6 is detected in each divided region. Then, it is assumed that the temporary exposure value α obtained from the luminance value y in each divided region is 10.96 Ev.

  In the digital camera of the present embodiment, the saturation limit value δ is defined as 2.0 Ev, so the saturation expected luminance value γ is γ = α + δ = 19.66 + 2.0 = 12.96 Ev.

  The comparison / counting processing unit 52 compares the luminance value y in each divided area with the saturation predicted luminance value γ = 12.96, and calculates the number of divided areas where the luminance value y exceeds the saturation predicted luminance value γ. The number of areas is measured as S. That is, the divided area where the luminance value y exceeds 12.96 Ev is detected, and the total number is counted.

  Here, in FIG. 6, since the area indicated by the white numbers is an area that exceeds the saturation expected luminance value γ, the number of these areas is measured and set as the saturation expected area number S. In the case of the example shown in FIG. 6, the number S of expected saturation areas is S = 25.

  For example, as shown in FIG. 8, the correction amount ε is calculated using the function F (S) in which the correction amount ε is defined according to the predicted saturation region number S. Is calculated. In the function F (S) shown in FIG. 8, when the number of predicted saturation areas S is 25, the correction amount ε is calculated as 0.21 Ev.

  Information on the calculated correction amount ε is output to the CPU 40, and the CPU 40 corrects the temporary exposure value α in accordance with the obtained information on the correction amount ε to obtain a final exposure value β. That is, the final exposure value β is calculated by adding the correction amount ε to the temporary exposure value α (β = α + ε). In the case of the above example, since the temporary exposure value α is α = 10.96Ev and the correction amount ε is ε = 0.21Ev, the final exposure value β is β = α + ε = 10.96 + 0.21 = 11.17Ev. Become.

  The CPU 40 determines the exposure based on the obtained final exposure value β. FIG. 7 is a list of numerical values obtained in the above exposure determination process.

  As described above, the correction amount ε is obtained according to the number of divided regions (the predicted saturation region number S) in which the luminance value y exceeds the saturated predicted luminance value γ, and the exposure value (temporary exposure value α) is corrected. Therefore, it is possible to suppress the occurrence of whiteout and obtain an image with good quality.

  The operation of the digital camera 10 of the present embodiment configured as described above is as follows.

  In the operation unit 50, when the mode of the digital camera 10 is set to the shooting mode and the power switch is pressed, the digital camera 10 is activated in the state of the shooting mode.

  When the digital camera 10 is activated in the photographing mode, the photographing lens 12 is extended to a predetermined photographing preparation position, image signal output from the CCD 14 is started, and a through image is displayed on the liquid crystal monitor 28. The photographer determines the composition by looking at the through image displayed on the liquid crystal monitor 28 and presses the shutter button halfway on the operation unit 50.

  When the shutter button is half-pressed, an S1 ON signal is input to the CPU 40. In response to the input of the S1 ON signal, the CPU 40 executes shooting preparation processing, that is, AE, AF, and AWB processing.

  First, the image signal output from the CCD 14 is subjected to necessary signal processing by the analog signal processing unit 16, then converted into a digital signal by the A / D converter 18, and taken into the RAM 44 via the image input controller 20. . Then, it is added to the AF detector 34 and the AE / AWB detector 36.

  The AF detection unit 34 calculates an integrated value necessary for AF control from the input image signal and outputs it to the CPU 40. The CPU 40 controls the photographing lens 12 based on the output from the AF detector 34 and focuses on the main subject.

  On the other hand, the AE / AWB detection unit 36 calculates an integrated value necessary for AE control and AWB control from the input image signal, that is, an integrated value of the image signal for each of R, G, and B for each preset divided region. (In the digital camera of the present embodiment, the integrated value of the image signal for each of R, G, and B in each divided region is calculated by dividing one screen into 64 (8 × 8) regions). Information on the calculated integrated value of the image signal for each of R, G, and B in each divided region is stored in the RAM 44.

  The CPU 40 adds the integrated values of the image signals for R, G, and B in each divided area calculated by the AE / AWB detection unit 36 to the white balance gain calculation circuit 22a and the light source type determination circuit 22j of the digital signal processing unit 22. Add.

  The white balance gain calculation circuit 22a calculates a gain value for white balance adjustment based on the integrated value of the image signals for each of R, G, and B in each divided area calculated by the AE / AWB detection unit.

  The light source type determination circuit 22j detects the light source type based on the integrated value of the image signals for each of R, G, and B in each divided region calculated by the AE / AWB detector 36.

  Further, the CPU 40 adds the integrated value of the image signals for each of R, G, and B in each divided area calculated by the AE / AWB detection unit 36 to the luminance calculation unit 38.

  The luminance calculation unit 38 integrates the integrated value of the image signal for each of R, G, and B in each divided area calculated by the AE / AWB detection unit 36, and the shooting conditions (aperture value, The photometric values r, g, and b for each of R, G, and B in each divided region are calculated based on the information on the shutter speed and the photographing sensitivity. Then, based on the obtained photometric values r, g, and b for each of R, G, and B in each divided region and the white balance adjustment gain values WBr, WBg, and WBb, the luminance value y in each divided region is calculated. calculate.

  The calculated luminance value y in each divided area is stored in the RAM 44.

  The CPU 40 calculates a temporary exposure value α from the calculated luminance value y in each divided region according to the currently set photometry mode. Then, the calculated temporary exposure value α is stored in the RAM 44.

  Further, the CPU 40 calculates a saturation predicted luminance value γ from the calculated temporary exposure value α. That is, the saturation expected brightness value γ is calculated by adding the saturation limit value δ (2 Ev in the digital camera of the present embodiment) to the calculated temporary exposure value α. Then, in order to obtain the correction amount ε to be applied to the temporary exposure value α, the calculated saturation expected luminance value γ and the information of the luminance value y in each divided region calculated by the luminance calculating unit 38 are compared / counted processing unit 52. Add to.

  The comparison / counting processing unit 52 compares the input luminance value y and the predicted saturation luminance value γ in each divided region, and determines the number of divided regions where the luminance value y exceeds the saturation predicted luminance value γ (saturation predicted region). The number S) is measured. Then, a correction amount ε corresponding to the calculated number S of expected saturation regions is calculated according to a predetermined function F (S) (see FIG. 8).

  Information on the calculated correction amount ε is output to the CPU 40, and the CPU 40 corrects the temporary exposure value α in accordance with the obtained information on the correction amount ε to obtain a final exposure value β. That is, the final exposure value β is calculated by adding the correction amount ε to the temporary exposure value α.

  When the correction value ε is 0, no correction is performed and the temporary exposure value α is used as it is as the final exposure value β.

  The CPU 40 determines the exposure (shooting sensitivity, aperture value, shutter speed) at the actual shooting from the calculated final exposure value β according to a predetermined program diagram.

  As described above, in the operation unit 50, when the shutter button is half-pressed, each control of AE, AF, and AWB is performed and preparation for photographing is performed.

  The photographer looks at the display on the liquid crystal monitor 28, confirms the angle of view, the focus state, and the like, and instructs the execution of photographing. That is, in the operation unit 50, the shutter button is fully pressed.

  When the shutter button is fully pressed, an S2 ON signal is input to the CPU 40. The CPU 40 executes the actual photographing process in response to the S2ON signal.

  First, the CCD 14 is exposed at the aperture value and shutter speed obtained as a result of the AE control, and a recording image is taken.

  The recording image signal output from the CCD 14 is subjected to required signal processing by the analog signal processing unit 16, and then converted into a digital signal by the A / D converter 18, and is sent to the RAM 44 via the image input controller 20. Stored. Then, it is added from the RAM 44 to the digital signal processing unit 22.

  The digital signal processing unit 22 performs necessary signal processing on the input image signal to generate an image signal (Y / C signal) composed of a luminance signal Y and color difference signals Cr and Cb.

  The luminance signal Y and the color difference signals Cr and Cb generated by the digital signal processing unit 22 are temporarily stored in the RAM 44 and then added to the compression / decompression processing unit 24.

  The compression / decompression processing unit 24 performs predetermined compression processing on the input image signal to generate compressed image data.

  The compressed image data generated by the compression / decompression processing unit 24 is stored in the RAM 44. The CPU 40 has a predetermined format image file in which predetermined shooting information (information related to shooting such as shutter speed, aperture value, shooting sensitivity, shooting mode, etc. at the time of shooting) is added to the compressed image data stored in the RAM 44. For example, an Exif format image file) is generated, and the image file generated via the recording control unit 30 is recorded on the storage medium 32.

  In this way, the image recorded on the storage medium 32 can be reproduced and displayed on the liquid crystal monitor 28 by setting the mode of the digital camera to the reproduction mode. That is, when the operation unit 50 sets the mode of the digital camera 10 to the playback mode, the compressed image data of the image file recorded last on the storage medium 32 is read and added to the compression / decompression processing unit 24. Then, after the compression / decompression processing unit 24 generates an uncompressed image signal, it is added to the VRAM 48 and is output from the VRAM 48 to the liquid crystal monitor 28 via the display control unit 26. As a result, the image recorded in the storage medium 32 is reproduced and displayed on the liquid crystal monitor 28. When the operation unit 50 performs an image frame advance operation, the next image is read from the storage medium 32, subjected to necessary signal processing, and reproduced and displayed on the liquid crystal monitor 28.

  As described above, in the digital camera 10 of the present embodiment, when the camera mode is set to the shooting mode and the shutter button is pressed halfway in the operation unit 50, AE, AF, AWB control is performed, and the shutter button When the button is fully pressed, the actual photographing is performed. When exposure is determined by AE control, the number of expected saturation areas S is measured, and a correction amount ε corresponding to the number of expected saturation areas S is obtained to obtain an exposure value ( Since the final exposure value (final exposure value β) is obtained by correcting the temporary exposure value α), whiteout is effective even when shooting a scene with a large luminance difference. Therefore, a high-quality image can be taken.

  That is, in the digital camera 10 of the present embodiment, as shown in FIG. 9, when determining the exposure, first, the luminance value y is individually obtained in each of the 64 (8 × 8) divided areas ( In step S10), a temporary exposure value α is obtained from the luminance value y for each divided area (step S11). Then, a saturation limit value δ is added to the obtained temporary exposure value α to obtain a saturation expected luminance value γ (step S12), and the obtained saturation expected luminance value γ is compared with the luminance value y in each divided region. (Step S13). Then, the number of divided regions where the luminance value y exceeds the saturation expected luminance value γ is measured to determine the saturation predicted region number S (step S14), and the correction amount ε is determined according to the calculated saturation predicted region number S. (Step S15). Then, the obtained correction amount ε is added to the temporary exposure value α to obtain the final exposure value β (step S16), and the exposure is determined from the obtained final exposure value β according to the program diagram (step S17). .

  Thereby, even when shooting a scene with a large luminance difference, the occurrence of whiteout can be effectively suppressed, and a high-quality image can be shot.

  In the present embodiment, when the correction amount ε is obtained from the number S of expected saturation regions, the correction amount ε is obtained using a predetermined function F (S) (see FIG. 8). The method for obtaining the quantity ε is not limited to this. For example, a table in which the correction amount ε is defined in accordance with the expected saturation region number S may be prepared in advance, and the correction amount ε may be obtained from the expected saturation region number S with reference to this table.

In addition, it is preferable that the function and table for obtaining the correction amount ε from the number S of expected saturation areas are optimized according to the subject. That is, for example, it is assumed that a luminance value y as shown in FIG. 6 is obtained by photographing the subject (photographing scene) shown in FIG. In this case, the maximum value of the luminance value y, that is, the maximum luminance value y _MAX is 13.35 Ev in the divided region (1, 3). In order to prevent overexposure of the image, it is sufficient that the maximum luminance value y _MAX is included in the dynamic range (latitude) at the photographic exposure (when further correction is performed, the photographic image is darkened). ). Therefore, a difference η (= 0.39 Ev) obtained by subtracting the saturation predicted luminance value γ (= 12.96 Ev) from the maximum luminance value y _MAX (= 13.35 Ev) may be obtained and set as the maximum correction amount. That is, the function F (S) and the table may be corrected or changed so that the difference η becomes the maximum value of the correction amount. For example, as shown in FIG. 10, the difference η (= 0.39 Ev) between the maximum luminance value y _MAX (= 13.35 Ev) and the saturation predicted luminance value γ (= 12.96 Ev) is the maximum correction amount ε. Thus, the function F (S) for obtaining the correction amount ε is corrected. Then, the correction amount ε is calculated based on the corrected function F ′ (S).

  As a result, the exposure value can be corrected more appropriately, and it is possible to effectively prevent the image from being darkened due to excessive exposure correction.

The function or table for obtaining the correction amount ε may be corrected or changed so that the difference η between the maximum luminance value y _MAX and the saturation expected luminance value γ becomes the maximum of the correction amount ε. The method is not particularly limited. For example, a function or table may be prepared for each difference η, and the function or table to be used may be changed according to the calculated difference η. Further, as shown in FIG. 11B, the function or the table may be corrected at a specific ratio according to the calculated difference η so that the calculated difference η becomes the maximum value. Furthermore, as shown in FIG. 11C, the upper limit of the function or table may be limited and corrected so that the calculated difference η becomes the maximum value (the difference η or more may be a constant value ( It is corrected so that it becomes the same value as the difference η).

  FIG. 12 is a flowchart showing a procedure for setting an exposure by optimizing a function (table) for obtaining the correction amount ε from the number S of predicted saturation regions.

As shown in the figure, first, in each divided area divided into 64 (8 × 8), a luminance value y is obtained individually (step S20), and a temporary exposure value α is calculated from the luminance value y for each divided area. Obtained (step S21). Then, the saturation limit value δ is added to the calculated temporary exposure value α to obtain the saturation expected luminance value γ (step S22), and the obtained saturation expected luminance value γ is compared with the luminance value y in each divided region. (Step S23), the number of divided regions where the luminance value y exceeds the saturated predicted luminance value γ (saturated predicted region number S) is obtained (Step S24). Thereafter, the maximum value of the luminance value y of each divided region, that is, the maximum luminance value y _MAX is obtained (step S25), and the difference η between the obtained maximum luminance value y _MAX and the saturation predicted luminance value γ is obtained (step S26). Then, the function F (S) for obtaining the correction amount ε is modified or changed so that the obtained difference η becomes the maximum value of the correction amount ε (step S27), and the corrected or changed function F ′ (S). Accordingly, a correction amount ε corresponding to the number S of expected saturation regions is obtained (step S28). Then, the obtained correction amount ε is added to the temporary exposure value α to obtain the final exposure value β (step S29), and the exposure is determined from the obtained final exposure value β according to the program diagram (step S30).

  As a result, the exposure value can be appropriately corrected, and a high-quality image can be taken even when a scene with a large luminance difference is taken.

  Next, a second embodiment of a digital camera to which the present invention is applied will be described.

  In the digital camera according to the first embodiment, the photographing region is divided into a plurality of regions, and the luminance value y is detected for each divided region, and the detected luminance value y exceeds the saturation expected luminance value γ. The number of division areas (saturation expected area number S) was obtained, and the correction amount ε was obtained according to the obtained saturation expected area number S.

  In the digital camera according to the present embodiment, the photographing area is divided into a plurality of areas, a photometric value is obtained for each R, G, and B for each divided area, and at least one of the obtained R, G, and B photometric values is obtained. Then, the number of divided areas exceeding the saturation expected luminance value γ ′ (saturation expected area number S ′) is obtained, and the correction amount ε is obtained according to the obtained saturation area number S ′. That is, if even one of the R, G, B photometric values r, g, b exceeds the saturation expected luminance value γ ′, color saturation occurs and an image with poor hue is taken. The number of divided areas where at least one of the photometric values r, g, b exceeds the saturation expected luminance value γ ′ (saturation expected area number S ′) is determined, and the correction amount ε is determined according to the determined saturation area number S ′ To ask. Thereby, even when shooting a scene with a large luminance difference, the occurrence of whiteout and color saturation can be effectively suppressed, and a high-quality image can be shot.

  Since the configuration other than the comparison / counting processing unit is the same as that of the digital camera of the first embodiment, only the configuration of the comparison / counting processing unit will be described here.

  FIG. 13 is a functional block diagram of the comparison / count processing unit 52 ′ of the digital camera according to the second embodiment.

  As described above, in the digital camera according to the present embodiment, the R, G, and B photometric values r, g, and b in each divided region are compared with the saturation expected luminance value γ ′, and R, G, B The number of divided regions (saturated expected region number S ′) in which at least one of the photometric values r, g, and b exceeds the saturation expected luminance value γ ′ is calculated. The photometric values r, g, and b for each of R, G, and B in the divided area and the saturation predicted luminance value γ ′ are input. The comparison / count processing unit 52 ′ compares the R, G, B photometric values r, g, b for each inputted divided region with the saturation expected luminance value γ ′, and R, G, B photometric values The number of divided regions in which at least one of r, g, and b exceeds the saturation predicted luminance value γ ′ is measured to determine the saturation predicted region number S ′. Then, using the function f (S ′) for calculating the correction amount ε, the correction amount ε is calculated from the obtained saturation predicted region number S ′.

  In the digital camera according to the present embodiment, the saturation expected luminance value γ ′ is calculated from the temporary exposure value α. That is, a predetermined saturation limit value δ ′ is added to the provisional exposure value α obtained from the luminance value y in each divided region to obtain a saturation expected luminance value γ ′. In the digital camera according to the present embodiment, the saturation limit value δ ′ is set to 2 Ev.

  Next, a procedure of photographing processing in the digital camera according to the second embodiment will be described.

  Since processing other than exposure setting is the same as that of the digital camera of the first embodiment, only the procedure for exposure setting will be described here.

  As described above, when the shutter button is half-pressed, the image signal output from the CCD 14 is subjected to necessary signal processing by the analog signal processing unit 16 and then the A / D converter 18 for determining the exposure. It is converted into a digital signal and taken into the RAM 44 from the image input controller 20. Then, it is added to the AE / AWB detection unit 36.

  The AE / AWB detection unit 36 calculates the integrated value of the image signal for each of R, G, and B for each divided region from the input image signal. Information on the calculated integrated value of the image signal for each of R, G, and B in each divided region is stored in the RAM 44.

  The CPU 40 adds the integrated value of the image signal for each of R, G, and B in each divided region calculated by the AE / AWB detection unit 36 to the luminance calculation unit 38. The luminance calculation unit 38 integrates the integrated value of the image signal for each of R, G, and B in each divided region calculated by the AE / AWB detection unit 36 and the shooting condition (aperture value, The photometric values r, g, and b for each of R, G, and B in each divided region are calculated based on the information on the shutter speed and the photographing sensitivity. Then, based on the obtained photometric values r, g, and b for each of R, G, and B in each divided region and the white balance adjustment gain values WBr, WBg, and WBb, the luminance value y in each divided region is calculated. calculate. The calculated luminance value y in each divided area is stored in the RAM 44.

  The CPU 40 calculates a temporary exposure value α from the calculated luminance value y in each divided region according to the currently set photometry mode. Then, the calculated temporary exposure value α is stored in the RAM 44.

  Further, the CPU 40 calculates a saturation predicted luminance value γ ′ from the calculated temporary exposure value α. That is, the saturation expected brightness value γ ′ is calculated by adding the saturation limit value δ ′ (= 2Ev) to the calculated temporary exposure value α. Then, the calculated saturation expected luminance value γ ′ and the photometric values r, g, and b for each of R, G, and B in each divided region are added to the comparison / count processing unit 52 ′.

  The comparison / counting processing unit 52 'compares the photometric values r, g, and b for each of the input divided areas R, G, and B with the saturation predicted luminance value γ'. Then, the number of divided areas in which at least one of the R, G, B photometric values r, g, b exceeds the saturation expected luminance value γ ′ is measured to obtain the saturation expected area number S ′. Then, a correction amount ε corresponding to the calculated expected saturation number S is calculated using a predetermined function f (S ′).

  Information on the calculated correction amount ε is output to the CPU 40, and the CPU 40 corrects the temporary exposure value α in accordance with the obtained information on the correction amount ε to obtain a final exposure value β. That is, the final exposure value β is calculated by adding the correction amount ε to the temporary exposure value α.

  When the correction value ε is 0, no correction is performed and the temporary exposure value α is used as it is as the final exposure value β.

  The CPU 40 determines the exposure (shooting sensitivity, aperture value, shutter speed) at the actual shooting from the calculated final exposure value β according to a predetermined program diagram.

  FIG. 14 is a flowchart showing a procedure for determining the exposure described above.

  As shown in the figure, first, photometric values r, g, and b are obtained for each of R, G, and B in each of the divided areas divided into 64 (8 × 8) (step S40). Then, the luminance value y in each divided region is obtained from the photometric values r, g, and b for each of the obtained divided regions (step S41), and provisional exposure is performed from the obtained luminance value y in the divided region. A value α is obtained (step S42). Then, the saturation limit value δ ′ is added to the obtained temporary exposure value α to obtain the saturation expected luminance value γ ′ (step S43), and the obtained saturation expected luminance value γ ′ and R, G in each divided region are obtained. , B are compared with the photometric values r, g, and b (step S44). Then, the number of divided areas in which at least one of the photometric values r, g, and b for each of R, G, and B exceeds the saturation expected luminance value γ ′ is measured to obtain the saturation expected area number S ′ (step S45). Then, the correction amount ε is obtained according to the obtained saturation predicted region number S ′ (step S46). Then, the obtained correction amount ε is added to the temporary exposure value α to obtain the final exposure value β (step S47), and the exposure is determined from the obtained final exposure value β according to the program diagram (step S48). .

  Hereinafter, a specific example will be described. For example, it is assumed that a subject (photographing scene) as shown in FIG. 15 is photographed, and photometric values r, g, and b for R, G, and B as shown in FIG. 16 are obtained in each divided region. Further, it is assumed that a luminance value y as shown in FIG. 17 is obtained in each divided region from the photometric results for each of R, G, and B in each divided region, and a temporary value obtained from the luminance value y in each divided region is obtained. Is assumed to be 13.19 Ev.

  In the digital camera of the present embodiment, the saturation limit value δ ′ is defined as 2.0 Ev, so the saturation expected luminance value γ ′ is γ ′ = α + δ ′ = 13.19 + 2.0 = 15.19 Ev. Become.

  The comparison / counting processing unit 52 ′ compares the photometric values r, g, and b for each of the divided regions with the predicted luminance value γ ′ = 15.19 for each of the R, G, and B, The number of divided areas in which at least one of the photometric values r, g, b exceeds the saturation expected luminance value γ ′ (saturation expected area number S ′) is measured. That is, a divided region in which at least one of the photometric values r, g, and b for each of R, G, and B exceeds the saturation expected luminance value γ ′ is detected, and the total number is counted.

  Here, in FIGS. 16A to 16C, the region displayed with white numbers is a region that exceeds the saturation expected luminance value γ, so the number of this region is measured, and the number of saturation predicted regions Let S ′. In the case of the example shown in FIG. 16, the number S ′ of saturation prediction regions is S ′ = 19.

  From the saturation predicted area number S ′ thus obtained, for example, as shown in FIG. 18, using the function f (S) in which the correction amount ε is defined according to the saturation expected area number S, the correction amount ε is calculated. In the function f (S) shown in FIG. 8, when the number of predicted saturation areas S ′ is 19, the correction amount ε is calculated as 0.18 Ev.

  Accordingly, the final exposure value β is obtained as 13.19 + 0.18 = 13.37 Ev from β = α + ε by adding the correction amount ε to the temporary exposure value α.

  Then, the exposure is set according to a predetermined program diagram from the final exposure value β thus obtained.

  As described above, in the digital camera of the present embodiment, the imaging region is divided into a plurality of regions, and the photometric values r, g, and b are obtained for each of the divided regions for each of R, G, and B, and the obtained R, G, and The number of divided regions (saturated expected region number S ′) in which at least one of the photometric values r, g, and b for each B exceeds the saturation predicted luminance value γ ′ is determined, and the number of saturated regions S ′ is determined. The correction amount ε is obtained, the temporary exposure value α is corrected, and the exposure is determined.

  Thereby, even when shooting a scene with a large luminance difference, the occurrence of whiteout and color saturation can be effectively suppressed, and a high-quality image can be shot.

  In the present embodiment, when the correction amount ε is obtained from the saturation predicted region number S ′, it is obtained using a predetermined function f (S ′). However, the digital camera of the first embodiment is used. Similarly to the above, the method for obtaining the correction amount ε from the number of predicted saturation regions S ′ is not limited to this. For example, the correction amount ε may be prepared in advance in accordance with the number of predicted saturation regions S ′, and the correction amount ε may be obtained from the number of predicted saturation regions S ′ with reference to this table.

As in the digital camera of the first embodiment, the function and table for obtaining the correction amount ε from the number of predicted saturation areas S ′ are preferably optimized according to the subject. That is, for example, it is assumed that the subject (photographing scene) shown in FIG. 15 is photographed and the photometric values r, g, and b for R, G, and B as shown in FIG. 16 are obtained in each divided region. In this case, the maximum value of the photometric values r, g, and b, that is, the maximum photometric value rgb _MAX is the B photometric value 15.51Ev in the divided region (3, 6). In order to prevent overexposure and color saturation of the image, it is sufficient that the maximum photometric value rgb _MAX is included in the dynamic range (latitude) in the exposure (when the correction is further performed, the captured image is darkened). .) Therefore, a difference η (= 0.32Ev) obtained by subtracting the saturation expected luminance value γ ′ (= 15.19Ev) from the maximum photometric value rgb _MAX (= 15.51Ev) may be obtained and set as the maximum correction amount. . That is, the function f (S ′) and the table may be corrected or changed so that the difference η becomes the maximum value of the correction amount. For example, as shown in FIG. 19, the difference η (= 0.32 Ev) between the maximum photometric value rgb _MAX (= 15.51 Ev) and the saturation predicted luminance value γ ′ (= 15.19 Ev) is the maximum correction amount ε. The function f (S ′) for obtaining the correction amount ε is corrected so that Then, the correction amount ε is calculated based on the corrected function f ′ (S ′).

  As a result, the exposure value can be corrected more appropriately, and it is possible to effectively prevent the image from being darkened due to excessive exposure correction.

The function or table for obtaining the correction amount ε may be corrected or changed so that the difference η between the maximum photometric value rgb _MAX and the saturation expected luminance value γ ′ becomes the maximum of the correction amount ε. The changing method is not particularly limited. For example, a function or table may be prepared for each difference η, and the function or table to be used may be changed according to the calculated difference η. Further, the function or the table may be corrected at a specific ratio according to the calculated difference η so that the calculated difference η becomes the maximum value (see FIG. 11B). Further, the upper limit of the function or table may be limited and corrected so that the calculated difference η becomes the maximum value (the difference η or more may be corrected to a constant value (the same value as the difference η)). (See FIG. 11 (c)).

  FIG. 20 is a flowchart showing a procedure for setting the exposure by optimizing a function (table) for obtaining the correction amount ε from the number of predicted saturation regions S ′.

As shown in the figure, first, in each divided region divided into 64 (8 × 8), photometric values r, g, and b for R, G, and B are obtained (step S50), and the obtained R, G, and B are obtained. The luminance value y in each divided region is obtained from the photometric values r, g, g for each B (step S51). Then, a temporary exposure value α is obtained from the luminance value y for each divided region (step S52), and a saturation limit value δ ′ is added to the obtained temporary exposure value α to obtain a saturation expected luminance value γ ′ ( Step S53). Then, the obtained saturation predicted luminance value γ ′ is compared with the photometric values r, g, b for each of R, G, B in each divided region (step S54), and at least one of the photometric values r, g, b is The number of divided areas (saturated expected area number S ′) exceeding the expected saturation brightness value γ ′ is obtained (step S55). Thereafter, the maximum value of the photometric values r, g, and b for each of the divided regions, that is, the maximum photometric value rgb _MAX is obtained (step S56), and the obtained maximum photometric value rgb _MAX and the saturation expected luminance value are obtained. A difference η from γ ′ is obtained (step S57). Then, the function f (S ′) for obtaining the correction amount ε is corrected or changed so that the obtained difference η becomes the maximum value of the correction amount ε, and saturated according to the corrected or changed function f ′ (S ′). A correction amount ε corresponding to the predicted area number S ′ is obtained (step S59). Then, the obtained correction amount ε is added to the provisional exposure value α to obtain the final exposure value β (step S60), and the exposure is determined from the obtained final exposure value β according to the program diagram (step S61).

  As a result, the exposure value can be appropriately corrected, and a high-quality image can be taken even when a scene with a large luminance difference is taken.

  As described above, as described in the series of embodiments, according to the present invention, by appropriately correcting the exposure value (temporary exposure value) obtained from the photometric result, it is possible to shoot a scene with a large luminance difference. Even in this case, it is possible to shoot a high-quality image without whiteout and color saturation.

  In the above embodiment, the case where the present invention is applied to a digital camera has been described as an example. However, the application of the present invention is not limited to this, and the present invention is also applied to a film camera using a so-called silver salt film. Can be applied.

  Further, in the above embodiment, the luminance value in each divided region is obtained by using the output of the image sensor used for photographing. However, a luminance sensor is separately installed and the luminance value in each divided region is obtained by this luminance sensor. May be requested.

  Similarly, a photometric sensor that measures light for each R, G, and B may be separately installed for each divided region, and a photometric value for each R, G, and B in each divided region may be obtained by this photometric sensor.

  The method for obtaining the temporary exposure value α from the photometric result is not particularly limited, and various methods can be used. For example, in addition to those exemplified in the above embodiment, various known methods such as a method using a histogram and a method for further correction can be adopted.

  Further, the user may input a value separately measured with an exposure meter.

  In the digital camera of the above embodiment, the content of the signal processing according to the present invention is configured by a hardware circuit, but the same function as that of the hardware circuit can be configured by software. That is, it can be configured by a predetermined control program.

  In the digital camera of the above embodiment, a CCD is used as an image sensor. However, the image sensor is not limited to this, and an image sensor such as a CMOS sensor may be used.

1 is a block diagram showing an electrical configuration of a digital camera according to a first embodiment 1 is a block diagram showing a schematic configuration of a digital signal processing unit in a digital camera according to a first embodiment. Functional block diagram of a luminance calculation unit in the digital camera of the first embodiment Functional block diagram of the comparison / counting unit in the digital camera of the first embodiment The figure which shows an example of a to-be-photographed object (shooting scene) The figure which shows an example of the measurement result of the brightness | luminance in each division area List of numerical values obtained during the exposure determination process The graph which shows an example of the function F (S) which calculates | requires correction amount (epsilon) from the number S of saturation prediction area | regions A flowchart showing an exposure determination procedure in the digital camera according to the first embodiment. The graph which shows an example of the function F '(S) optimized from the luminance maximum value The figure which shows the example of correction | amendment of the function F (S) which calculates | requires correction amount (epsilon) The flowchart which shows the process sequence in the case of optimizing the function F (S) which calculates | requires correction amount (epsilon), and setting exposure. Functional block diagram of the comparison / counting processing unit in the digital camera of the second embodiment The flowchart which shows the procedure of the exposure setting in the digital camera of 2nd Embodiment The figure which shows an example of a to-be-photographed object (shooting scene) The figure which shows an example of the photometry result for every R, G, B in each division area The figure which shows an example of the measurement result of the brightness | luminance in each division area The graph which shows an example of the function f (S) which calculates | requires correction amount (epsilon) from the saturation expected area number S ' The figure which shows the example of correction | amendment of the function f (S ') which calculates | requires correction amount (epsilon). The flowchart which shows the process sequence in the case of optimizing the function f (S ') which calculates | requires correction amount (epsilon), and setting exposure.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Digital camera, 12 ... Shooting lens, 14 ... Image sensor, 16 ... Analog signal processing part, 18 ... A / D converter, 20 ... Image input controller, 22 ... Digital signal processing part, 24 ... Compression / decompression processing part , 26 ... display control section, 28 ... liquid crystal monitor, 30 ... recording control section, 32 ... storage medium, 34 ... AF detection section, 36 ... AE / AWB detection section, 38 ... luminance calculation section, 40 ... CPU, 42 ... ROM , 44 ... RAM, 46 ... flash memory, 48 ... VRAM, 50 ... operating unit, 52, 52 '... comparison / counting processing unit, 54 ... bus

Claims (6)

In an imaging device that determines the exposure based on the exposure value obtained from the photometric result of the subject,
A saturation expected luminance value calculating means for calculating a luminance value expected to be saturated based on the exposure value as a saturation predicted luminance value;
A luminance value detecting means for dividing the photographing region into a plurality of regions and detecting a luminance value for each divided region;
A saturation expected area number detecting means for detecting, as the saturation expected area number, the number of divided areas in which the brightness value detected by the brightness value detecting means exceeds the saturation expected brightness value;
A correction amount acquisition means for acquiring a correction amount according to the number of expected saturation regions using a predetermined function or table;
Exposure value correction means for correcting the exposure value with the correction amount acquired by the correction amount acquisition means;
An imaging apparatus comprising: Maximum brightness value detection means for detecting the maximum brightness value as the maximum brightness value among the brightness values detected for each divided region by the brightness value detection means;
A correction unit that calculates a difference between the maximum luminance value detected by the maximum luminance value detection unit and the saturation expected luminance value, and corrects or changes the function or table so that the calculated difference becomes a maximum value of a correction amount; ,
The imaging apparatus according to claim 1, further comprising:   The photographing apparatus according to claim 1, wherein an exposure value is obtained based on a luminance value detected for each divided region by the luminance value detecting unit. In an imaging device that determines the exposure based on the exposure value obtained from the photometric result of the subject,
A saturation expected luminance value calculating means for calculating a luminance value expected to be saturated based on the exposure value as a saturation predicted luminance value;
A photometric unit that divides the imaging region into a plurality of regions and performs photometry for each of the divided regions for each of R, G, and B;
A predicted saturation region number detection unit for detecting, as a saturation prediction region number, the number of divided regions in which at least one of the R, G, and B photometry values measured by the photometry unit exceeds the saturation prediction luminance value;
A correction amount acquisition means for acquiring a correction amount according to the number of expected saturation regions using a predetermined function or table;
Exposure value correction means for correcting the exposure value with the correction amount acquired by the correction amount acquisition means;
An imaging apparatus comprising: A maximum photometric value detecting means for detecting a maximum photometric value as a maximum photometric value among the photometric values for each of R, G, and B measured for each divided area by the photometric detecting means;
A correction unit that calculates a difference between the maximum photometric value detected by the maximum photometric value detection unit and the saturation expected luminance value, and corrects or changes the function or table so that the calculated difference becomes a maximum value of a correction amount; ,
The imaging apparatus according to claim 4, further comprising:   6. The photographing apparatus according to claim 4, wherein an exposure value is obtained based on a photometric value for each of R, G, and B that is measured for each divided region by the photometric means.

Images