JP2007027943A - Imaging apparatus, program and method for processing shading - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To deal with shading appropriately by judging whether a scene is susceptible to shading or not precisely. <P>SOLUTION: Out of 256 blocks obtained by dividing a pixel acquired by an imaging element into sixteen in the longitudinal/lateral direction, 156 blocks on the periphery of an image is used for counting the number of blocks of sky blue sky_num. After setting an exposure correction value D_BV_SKY depending on the number of blocks of sky blue sky_num, that exposure correction value is reflected on exposure setting during exposure. Since exposure correction is performed, based on the rate of sky blue region detected from the periphery of an image, one scene susceptible to shading, i.e. a scene where the sky is reflected on the greater part of an image, can be judged precisely and reduction in shading can be dealt with appropriately. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a technique of an imaging apparatus that acquires an image related to a subject.

  For image processing on images taken with a digital camera (imaging device), etc., the shooting scene is determined by a histogram based on photometric information and colorimetric information at the center of the image, and shading correction is applied according to the shooting scene. A technique is known (for example, Patent Document 1).

JP 2004-88408 A

  However, in the technique of the above-described Patent Document 1, a shooting scene is determined based on photometric / colorimetric information at the center of the image, but it is accurate to determine whether the scene is really susceptible to shading from information only at the center of the image. Not always good. This makes it difficult to appropriately deal with shading.

  Further, in the conventional shading correction which is a known technique, the gain at the peripheral portion of the image is forcibly increased by an LUT or the like, and color noise such as spots may appear in the peripheral portion.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a technique for an imaging apparatus that can accurately determine whether a scene is easily affected by shading and perform an appropriate response.

  In order to solve the above-described problems, the invention of claim 1 is an imaging apparatus, wherein (a) an imaging unit that acquires an image relating to a subject, and (b) a dividing unit that divides the image into a plurality of regions. (C) based on photometric information and / or colorimetric information relating to each of the plurality of regions, detection means for detecting the degree of shading related to the image, and (d) exposure control according to the degree of influence of the shading, and And / or means for performing image processing, and the image processing is processing that does not depend on pixel positions related to the image.

  The invention of claim 2 is an imaging apparatus, wherein (a) an imaging means for acquiring an image relating to a subject, (b) a dividing means for dividing the image into a plurality of regions, and (c) the plurality of the plurality of areas. A photometric means for obtaining photometric information relating to each of the areas; (d) a colorimetric means for obtaining colorimetric information relating to each of the plurality of areas; and (e) the photometric information and / or the colorimetric information, Detection means for detecting the degree of shading related to the image; (f) correction amount calculation means for calculating a correction amount according to the degree of influence of shading; and (g) exposure control and / or image based on the correction amount. Means for performing processing, and the image processing is processing independent of a pixel position related to the image.

  According to a third aspect of the present invention, in the imaging apparatus according to the first or second aspect of the present invention, the colorimetric information is color difference information relating to YCrCb.

  According to a fourth aspect of the present invention, in the imaging apparatus according to any one of the first to third aspects of the present invention, the detection means determines the degree of influence of the shading based on a sky blue region that occupies the periphery of the image. It has a means to detect.

  According to a fifth aspect of the present invention, in the imaging apparatus according to any one of the first to fourth aspects, the detection unit is configured to perform the shading based on a high-luminance white region occupying a peripheral portion of the image. Means for detecting the degree of influence.

  According to a sixth aspect of the present invention, in the imaging apparatus according to any one of the first to fifth aspects of the present invention, the detection means is based on a specific area occupying the periphery of the image, and the degree of influence of the shading. The specific area is an area of a neighboring color related to the specific color.

  According to a seventh aspect of the present invention, in the imaging apparatus according to any one of the first to sixth aspects, the detection means has a maximum luminance in the entire image obtained from photometric information of each of the plurality of regions. Means for detecting the degree of influence of the shading based on the difference from the minimum luminance.

  According to an eighth aspect of the present invention, in the imaging apparatus according to the second aspect of the present invention, in the exposure control, exposure correction is performed according to the correction amount.

  According to a ninth aspect of the present invention, in the image pickup apparatus according to the second aspect of the present invention, in the exposure control, a correction for setting an aperture value to a narrowing side is performed according to the correction amount.

  The invention according to claim 10 is the imaging apparatus according to claim 2, further comprising: (h) selection means for selecting one tone curve from a plurality of tone curves based on the correction amount; Is image processing using one tone curve selected by the selection means.

  According to an eleventh aspect of the present invention, in the imaging apparatus according to the second aspect of the invention, the correction amount calculating means includes (f-1) an adjusting means for adjusting the correction amount in accordance with a focal length of the photographing lens. .

  A twelfth aspect of the invention is a program for causing an imaging device to function as the imaging device according to any one of the first to eleventh aspects of the invention when executed by a computer built in the imaging device.

  The invention of claim 13 is a method for performing processing relating to shading, wherein an imaging step for acquiring an image relating to a subject, a division step for dividing the image into a plurality of regions, and photometry for each of the plurality of regions. A photometric step for generating information, a colorimetric step for generating colorimetric information for each of the plurality of regions, and a detection for detecting an influence of shading on the image based on the photometric information and / or the colorimetric information. A correction amount calculation step of calculating a correction amount according to the degree of influence of the shading, and a processing step of performing exposure control and / or image processing based on the correction amount, wherein the image processing is performed on the image. This process is independent of the pixel position.

  According to the first to thirteenth aspects of the present invention, based on photometric information and / or colorimetric information regarding each of a plurality of regions obtained by dividing the image acquired by the imaging unit, the degree of shading related to the image is detected, Exposure control according to the degree of influence of shading and / or image processing independent of the pixel position of the image is performed. As a result, it is possible to accurately determine whether or not the scene is easily affected by shading and perform an appropriate response.

  In particular, in the invention of claim 3, since the colorimetric information is color difference information regarding YCrCb, it is possible to quickly obtain the colorimetric information while reducing the calculation burden.

  In the invention of claim 4, since the influence degree of shading is detected based on the sky blue area in the peripheral portion of the image, it is possible to accurately determine a scene that is easily affected by shading, for example, contains a lot of blue sky.

  In the invention of claim 5, since the degree of influence of shading is detected based on a high-luminance white area occupying the peripheral portion of the image, a scene that is easily affected by shading, for example, a lot of snow scenes is accurately detected. Can be judged.

  In the invention of claim 6, since the influence degree of the shading is detected based on the neighboring color region relating to the specific color in the peripheral portion of the image, a scene that is easily affected by the shading and has little color variation is accurately detected. Can judge well.

  In the invention of claim 7, since the degree of influence of shading is detected based on the difference between the maximum luminance and the minimum luminance in the entire image obtained from the photometric information of each of the plurality of areas, the low sensitivity to the influence of shading is low. Contrast scenes can be accurately determined.

  In the eighth aspect of the invention, since exposure correction is performed according to the correction amount in exposure control, the influence of shading can be reduced regardless of image processing.

  In the invention of claim 9, since exposure control performs correction for setting the aperture value to the aperture side in accordance with the correction amount, the influence of shading can be reduced regardless of image processing.

  In the invention of claim 10, since the image processing is image processing using one tone curve selected from a plurality of tone curves based on the correction amount, the influence of shading can be quickly reduced.

  In the invention of claim 11, since the correction amount is adjusted according to the focal length of the photographing lens, the influence of shading can be reduced appropriately.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<Configuration of Imaging Device 1>
1 to 3 are diagrams illustrating a schematic configuration of an external appearance of an imaging apparatus 1 according to an embodiment of the present invention. 1 is a plan view of the image pickup apparatus 1, FIG. 2 is a cross-sectional view taken from the position II-II in FIG. 1, and FIG.

  The imaging device 1 is configured as a digital camera, for example, and includes a camera body 2 that has a substantially rectangular parallelepiped shape and a photographing lens 3 that is detachably attached to the camera body 2. As shown in FIG. 1, the imaging apparatus 1 is configured so that a memory card 8 for recording a captured image is detachably accommodated. In addition, the imaging device 1 uses a power supply battery E that connects four AA batteries E1 to E4 in series as a drive source.

  As shown in FIG. 2, the photographing lens 3 that is a zoom lens includes a lens group 30. Here, a two-group zoom lens is shown as the photographing lens 3, and the lens group 30 is roughly classified into two lens groups 300 and 301. 2 and 3, each of the lens groups 300 and 301 is shown as a single lens for convenience of illustration. However, actually, each lens group 300, 301 is not limited to a single lens, and may be configured as an aggregate of a plurality of lenses.

  On the other hand, a motor M1 for driving the lens group 300 and a motor M2 for driving the lens group 301 are provided inside the camera body 2. By controlling these motors M1 and M2, it is possible to change the zoom magnification of the photographic lens 3 and change the focus state of the photographic lens 3 (that is, the focus operation).

  In addition, a color image sensor 303 that acquires an image related to the subject is provided at an appropriate position behind the lens group 30 of the photographic lens 3. The color image sensor 303 is a single-plate color area sensor in which R (red), G (green), and B (blue) color filters are attached in a checkered pattern on the surface of each pixel of an area sensor composed of a CCD. Composed.

  As shown in FIG. 1, a grip part G is provided on the front surface of the camera body 2, and a pop-up built-in flash 5 is provided at an appropriate position at the upper end of the camera body 2. As shown in FIG. 3, a shutter button 9 is provided on the upper surface of the camera body 2. The shutter button 9 has a function of detecting and discriminating a half-pressed state (S1) used as a trigger for focus adjustment or the like and a full-pressed state (S2) used as a trigger for recording photographing (main photographing). I'm doing it.

  On the other hand, an electronic viewfinder (hereinafter “EVF”) 20 and a liquid crystal display (hereinafter “LCD”) 10 are provided on the back of the camera body 2. Unlike the optical viewfinder, the EVF 20 and the LCD 10 that perform live view display of the image signal from the CCD 303 in the shooting standby state serve as a viewfinder.

  Further, the LCD 10 can display a menu screen for setting a shooting mode, shooting conditions, and the like in the recording mode, and can reproduce and display a captured image recorded in the memory card 8 in the reproduction mode.

  A power switch 14 is provided on the rear left side of the camera body 2. The power switch 14 also serves as a mode setting switch for switching between a recording mode (a mode for performing a photography function) and a reproduction mode (a mode for reproducing a recorded image on the LCD 10). That is, the power switch 14 is a three-point slide switch. When the contact is set to the center “OFF” position, the power is turned off. When the contact is set to the upper “REC” position, the power is turned on and the recording mode is set. When the contact is set to the lower “PLAY” position, the power is turned on and the playback mode is set.

  A quadruple switch 15 is provided on the right side of the back surface of the camera body 2. The quadruple switch 15 has a circular operation button, and various operations can be performed by pressing buttons SU, SD, SL, and SR in four directions of up, down, left, and right in this operation button. For example, it functions as a switch for changing the item selected on the menu screen displayed on the LCD 10 or changing the frame to be reproduced selected on the index screen. In the recording mode, the left and right buttons SL and SR function as switches for changing the zoom magnification. Specifically, the zoom magnification is changed by changing the relative positional relationship between the two lens groups 300 and 301 by driving the motors M1 and M2. More specifically, when the right switch SR is pressed, the camera moves continuously to the wide side, and when the left switch SL is pressed, the camera moves continuously to the tele side.

  A switch group 16 such as a cancel switch 33, an execution switch 32, a menu display switch 34, and an LCD display switch 31 is provided below the quadruple switch 15. The cancel switch 33 is a switch for canceling the content selected on the menu screen. The execution switch 32 is a switch for confirming or executing the content selected on the menu screen. The menu display switch 34 is a switch for displaying a menu screen on the LCD 10 and switching the contents of the menu screen. The LCD display switch 31 is an on / off switch for displaying on the LCD 10.

  Next, the internal configuration of the imaging apparatus 1 will be described. FIG. 4 is a schematic block diagram illustrating the internal configuration of the imaging apparatus 1.

  The taking lens 3 includes a lens group 300, 301 and a diaphragm 302 for adjusting the amount of transmitted light. In FIG. 4, for convenience of illustration, the diaphragm 302 is shown to be disposed on the rear side of the lens group 301, but the arrangement of the diaphragm 302 is not limited to this. For example, the diaphragm 302 may be provided inside the lens group 301 (or 300), or may be provided between both lens groups 300 and 301.

  The CCD 303 receives light from a subject incident through the photographing lens 3 for a predetermined exposure time, and photoelectrically converts it into an image signal and takes it in. The CCD 303 outputs the image signal after photoelectric conversion to the signal processing unit 120. In this way, the subject image from the photographing lens 3 as the photographing optical system is acquired as an image.

  The signal processing unit 120 performs predetermined analog signal processing and digital signal processing on the image signal output from the CCD 303. The signal processing of the image signal is performed for each light reception signal of each pixel constituting the image data. The signal processing unit 120 includes an analog signal processing circuit 121, an A / D conversion circuit 122, a shading correction circuit 123, an image processing circuit 124, and an image memory 126.

  The analog signal processing circuit 121 performs analog signal processing. The analog signal processing circuit 121 mainly includes a CDS (correlated double sampling) circuit and an AGC (auto gain control) circuit, and reduces the sampling noise of the pixel signal output from the CCD 303 and the signal. Adjust the level.

  The A / D conversion circuit 122 converts a pixel signal (image signal) that is an analog signal output from the analog signal processing circuit 121 into pixel data (image data) that is a digital signal. The A / D conversion circuit 122 converts the pixel signal received by each pixel into, for example, a 12-bit digital signal and sets it as pixel data having a gradation value of 0 to 4095. The converted pixel data (image data) is temporarily stored in the image memory 126.

  The shading correction circuit 123 corrects shading (a reduction in the amount of light around the image) by the optical system for the A / D converted pixel data. Specifically, the shading correction is performed by multiplying the image data converted by the A / D conversion circuit 122 and the shading correction coefficient in which the gain of the peripheral portion of the image is set higher than that of the central portion.

  The image processing circuit 124 includes a WB (white balance) circuit, a color balance evaluation circuit, a pixel interpolation circuit, a color correction circuit, a γ correction circuit, a color separation circuit, a spatial filter, a resolution conversion circuit, a compression / decompression processing circuit, and the like. Yes. Of these, the WB circuit is for adjusting the white balance of the photographed image. The WB circuit converts the level of the pixel data of each color component of R, G, and B using the evaluation result on the color balance of the photographed image by the color balance evaluation circuit. In the CCD 303 having a Bayer array in which three types of color filters of R, G, and B are dispersedly arranged, the pixel interpolating circuit includes two of the three color components R, G, and B that do not actually exist in each pixel position. The color component is obtained by interpolation, and the color correction circuit is a circuit that corrects the spectral sensitivity characteristic of the filter. The γ correction circuit is a circuit that corrects the γ characteristic of the pixel data, and corrects the level of each pixel data using a preset γ correction table. The color separation circuit is a circuit that converts (R, G, B) signals into (Y, Cr, Cb) signals. This color separation processing is performed using a matrix calculator. The spatial filter is a circuit that performs various types of filter processing such as edge enhancement using a low-pass filter and a high-pass filter. The resolution conversion circuit is a circuit that converts to a desired resolution, and the compression / decompression processing circuit is a circuit that performs compression processing to data of a predetermined format such as JPEG and vice versa.

  The image memory 126 is a memory for temporarily storing image data. Each process in the image processing circuit 124 is performed on the image data stored in the image memory 126.

  The light emission control unit 102 controls the light emission of the flash 5 based on the light emission control signal input from the overall control unit 150.

  The lens control unit 130 controls the driving of the lens groups 300 and 301 and the diaphragm 302 in the photographing lens 3. The lens control unit 130 drives the aperture control circuit 131 that controls the aperture value of the aperture 302, the zoom control circuit 132 that changes the zoom magnification by driving the motors M1 and M2, and the motors M1 and M2. And a focus control circuit 133 for performing focus control.

  The aperture control circuit 131 drives the aperture 302 based on the aperture value input from the overall control unit 150, and sets the aperture amount to the aperture value. The focus control circuit 133 controls the driving amounts of the motors M1 and M2 based on the AF control signal input from the overall control unit 150, and sets the lens groups 300 and 301 to the focal position. The zoom control circuit 132 drives the motors M1 and M2 to move the lens groups 300 and 301 based on a zoom control signal input from the overall control unit 150 in response to an input from the quad switch 15. As a result, the zoom state moves to the wide side or the tele side.

  The display unit 140 performs display on the LCD 10 and the EVF 20. In addition to the LCD 10 and the EVF 20, the display unit 140 includes an LCD VRAM 141 serving as a buffer memory for image data reproduced and displayed on the LCD 10, and an EVF VRAM 142 serving as a buffer memory for image data reproduced and displayed on the EVF 20.

  In the photographing standby state, each pixel data of an image (live view image) photographed by the CCD 303 every 1/30 (seconds) is subjected to predetermined signal processing by the signal processing unit 120, and then the image memory 126. Is temporarily stored. Then, the data is read out by the overall control unit 150, adjusted in data size, transferred to the LCDVRAM 141 and EVFVRAM 142, and displayed on the LCD 10 and EVF 20 as a live view display. Thereby, the user can visually recognize the subject image. In the playback mode, the image read from the memory card 8 is subjected to predetermined signal processing by the overall control unit 150, then transferred to the LCD VRAM 141, and played back and displayed on the LCD 10.

  The operation unit 101 inputs operation information of operation members related to photographing and reproduction provided in the camera body unit 2 described above to the overall control unit. The operation information input from the operation unit 101 includes operation information of each operation member such as the shutter button 9, the power switch 14, the quad switch 15, and the switch group 16.

  The overall control unit 150 is composed of a microcomputer and centrally controls the photographing function and the reproduction function. The memory card 8 is connected to the overall control unit 150 via the card interface 103. A personal computer PC is externally connected via the communication interface 105.

  The overall control unit 150 includes a ROM 151 that stores a processing program for performing a number of specific processes in the photographing function and a reproduction function, and a control program for controlling the driving of each member of the imaging apparatus 1 described above, and a processing A RAM 152 is provided as a work area for performing various arithmetic operations according to the program and the control program. Note that program data such as a program for performing shading correspondence processing (hereinafter referred to as “shading correspondence program”) recorded in the memory card 8 as a recording medium is read via the card interface 103 and stored in the ROM 151. Be able to. Therefore, these processing program and control program can be installed in the imaging apparatus 1 from the memory card 8. The processing program and the control program may be installed from the personal computer PC via the communication interface 105.

  The operation of the imaging apparatus 1 having the above configuration will be described in detail.

<Operation of Imaging Device 1>
FIG. 5 is a flowchart showing the basic operation of the imaging apparatus 1. This operation particularly corresponds to a corresponding process related to shading, and is executed by the control unit 150 executing a shading compatible program for performing this process.

  In the state where the shooting mode is set and the live view shooting is performed, it is determined whether the shutter button 9 is half-pressed by the user (step ST1). Here, if half-pressed, the process proceeds to step ST2, and if not half-pressed, step ST1 is repeated.

  In step ST2, photographing conditions are acquired. That is, various types of information necessary for actual photographing, such as the focal length of the photographing lens 3, information on the aperture 302, and ISO sensitivity setting information, are acquired.

  In step ST3, photometric / colorimetric information is acquired from image data acquired by the CCD 303 by live view shooting (detailed later).

  In step ST4, a control exposure level is calculated based on the photometric / colorimetric information acquired in step ST3 (details will be described later).

  In step ST5, based on the photometric / colorimetric information acquired in step ST3, it is determined whether or not the scene is susceptible to shading (detailed later).

  In step ST6, exposure correction is performed as a measure for reducing shading according to the degree of influence of shading detected in step ST5 (details will be described later).

  In step ST7, control exposure is set based on the exposure correction in step ST6 (details will be described later).

  In step ST8, it is determined whether the shutter button 9 has been fully pressed by the user. Here, if it is fully pressed, the process proceeds to step ST9. If it is not fully pressed, the process returns to step ST1.

  In step ST9, exposure is performed with the control exposure set in step ST7.

  In step ST10, photometric / colorimetric information is acquired from the image data acquired by the CCD 303 by the exposure in step ST9 (detailed later).

  In step ST11, an appropriate tone curve is selected as a measure for reducing shading according to the degree of influence of shading detected based on the photometric / colorimetric information acquired in step ST10.

  In step ST12, an image is recorded. That is, an image that has been subjected to image processing using the tone curve selected in step ST11 is recorded in the memory card 8.

  FIG. 6 is a flowchart corresponding to the above-described step ST3 (ST10) and showing the photometric / colorimetric information acquisition operation.

  In step ST21, photometric information and colorimetric information relating to a block obtained by dividing the image acquired by the CCD 303 are acquired. This will be specifically described.

  As shown in FIG. 7, the image Go acquired by the CCD 303 is divided into 16 parts in the vertical direction and the horizontal direction, respectively, and 256 blocks Bk are generated as a plurality of areas. The photometric information Y [i] (i = 0 to 255) and the colorimetric information R [i], G [i], and B [i] (i = 0 to 255) are 12-bit data for each block Bk. get. As the photometric information and colorimetric information, for example, an average luminance value and an average colorimetric value in each block Bk are used.

  In step ST22, color difference information for each block Bk is acquired based on the photometric information and colorimetric information obtained in step ST21. Specifically, the color difference information CrS and CbS related to the YCrCb color space is calculated as in the following expressions (1) and (2).

CrS [i] = k1 × (R [i] −Y [i]) / 16 (1):
CbS [i] = k1 × (B [i] −Y [i]) / 16 (2):
Here, k1 on the right side of the above formulas (1) to (2) is set to a value larger than “0” (for example, “1”).

  In step ST23, the maximum luminance and the minimum luminance relating to the block Bk are detected in the entire image. Specifically, the maximum luminance cell_max and the minimum luminance cell_min are detected from 256 pieces of photometric information Y [i] (i = 0 to 255) acquired in step ST21.

  FIG. 8 is a flowchart corresponding to the above-described step ST4 and showing the exposure level calculation operation.

  In step ST31, based on luminance information obtained from image data captured by the CCD 303, a photographing scene such as backlight or direct light is determined using a known method.

  In step ST32, the optimal control luminance is calculated based on the shooting scene determined in step ST31. Specifically, the control luminance BVtgt is calculated as in the following equation (3).

BVtgt = f (Y [i], shooting scene information, other information) (3):
That is, the control brightness BVtgt is brightness information Y [i] of the entire image, information of the shooting scene obtained in step ST31, and other information (for example, focus position, distance to the subject, focal length information) Is obtained by a function f having an argument of

  FIG. 9 is a flowchart corresponding to the above-described step ST5 and showing the scene determination operation.

  In step ST41, a sky blue area is detected at the periphery of the image. This specific detection method will be described below.

  First, an image Go composed of 256 blocks Bk shown in FIG. 7 is divided into an image central region CP composed of 100 blocks Bk arranged in the central portion (in the bold frame in the figure), and other than the image central region CP. Are divided into an image peripheral area EP composed of 156 blocks Bk.

  Then, among the 156 blocks Bk in the image peripheral area EP, the number sky_num of sky blue blocks Bk satisfying the following condition is counted.

85 ≦ CrS [i] ≦ 127:
132 <CbS [i] ≦ 188:
640 <Y [i]:
As described above, the influence of shading can be detected by detecting the sky blue area in the image peripheral area EP.

  In step ST42, a white area with high luminance is detected at the periphery of the image, for example, an area where a snow scene is reflected. This specific detection method will be described below.

  Among the 156 blocks Bk in the image peripheral area EP shown in FIG. 7, the number snow_num of the blocks Bk satisfying the following condition is counted.

120 <CrS [i] <136:
124 <CbS [i] <132:
・ 3200 <Y [i]:
As described above, by detecting the high brightness white area in the image peripheral area EP, the influence degree of shading can be detected.

  In step ST43, the color average of the peripheral portion of the image is calculated. Specifically, an average value crs_ave of CrS [i] and an average value cbs_ave of CbS [i] are obtained for 156 blocks Bk in the image peripheral area EP shown in FIG.

  In step ST44, an area of a specific color (hereinafter also referred to as “uniform uniform color area”) with small color variation and high uniformity is detected in the peripheral portion of the image. This specific detection method will be described below.

  Among the 156 blocks Bk in the image peripheral area EP shown in FIG. 7, the number monocol_num of the blocks Bk satisfying the following condition is counted.

CrS [i] is within crs_ave ± 6 calculated in step ST43:
CbS [i] is within cbs_ave ± 6 calculated in step ST43:
As described above, the degree of influence of shading can be detected by detecting the neighboring color region relating to the average color (specific color) in the image peripheral region EP.

  FIG. 10 is a flowchart corresponding to the above step ST6 and showing the exposure correction operation.

  In step ST51, an exposure correction value is calculated according to the ratio of the sky blue area detected in step ST41 to the image peripheral area EP. A method for calculating the exposure correction value will be described below.

  FIG. 11 is a diagram showing the relationship between the sky blue area and the exposure correction value. In FIG. 11, the horizontal axis indicates the number of sky blue area blocks sky_num (maximum value is 156), and the vertical axis indicates the exposure correction value D_BV_SKY.

  As shown in the graph Ha, the exposure correction value D_BV_SKY starts to increase from 32 in the number of blocks in the sky blue area, and becomes constant at the maximum value of 0.375 EV when reaching 82.

  In this way, by setting the exposure correction value in the overexposed direction in accordance with the occupied area of the sky blue region with respect to the image peripheral region EP, shading of the scene or the like in which the sky Bs shown in FIG. Reduction can be achieved (described later).

  In step ST52, an exposure correction value is calculated according to the ratio of the high brightness white area detected in step ST42 to the image peripheral area EP. A method for calculating the exposure correction value will be described below.

  FIG. 13 is a diagram showing the relationship between the high brightness white area and the exposure correction value. In FIG. 13, the horizontal axis represents the number of blocks in the high brightness white area, snow_num (maximum value is 156), and the vertical axis represents the exposure correction value D_BV_SNOW.

  As shown in the graph Hb, the exposure correction value D_BV_SNOW starts to increase from 24 in the high brightness white area block number snow_num, and becomes constant at the maximum value of 0.5 EV when it reaches 72.

  In this way, by setting the exposure correction value in the overexposed direction in accordance with the area occupied by the high-intensity white region with respect to the image peripheral region EP, shading can be reduced for a scene or the like in which the snow scene Bw shown in FIG. Can be achieved (described later).

  In step ST53, an exposure correction value is calculated according to the ratio of the uniform specific color area detected in step ST44 to the peripheral image area EP. A method for calculating the exposure correction value will be described below.

  FIG. 15 is a diagram illustrating the relationship between the uniform specific color region and the exposure correction value. In FIG. 15, the horizontal axis indicates the number of blocks monocol_num (maximum value is 156) in the uniform specific color region, and the vertical axis indicates the exposure correction value D_BV_MONO.

  As shown in the graph Hc, the exposure correction value D_BV_MONO starts to increase from the number of blocks monocol_num of the uniform specific color region from 40, and when it reaches 92, becomes constant at the maximum value of 0.375EV.

  As shown in the graph Hc, by setting the exposure correction value in the overexposed direction according to the occupation area of the uniform specific color region with respect to the image peripheral region EP, the grass Bg of the baseball field shown in FIG. Shading can be reduced for a scene or the like (described later).

  In step ST54, a contrast difference regarding the entire image is calculated. Specifically, the contrast difference (luminance difference) D_BV_CELL is calculated using the maximum luminance cell_max and the minimum luminance cell_min detected in step ST23 as shown in the following equation (4).

D_BV_CELL = cell_max−cell_min (4):
When D_BV_CELL calculated by the above equation (4) is small, it can be determined that the scene is a low-contrast scene that is easily affected by shading. That is, the influence degree of shading can be detected based on the difference between the maximum luminance and the minimum luminance in the entire image obtained from the photometric information of each block Bk.

  In step ST55, an exposure correction value is calculated according to the contrast difference calculated in step ST54. A method for calculating the exposure correction value will be described below.

FIG. 17 is a diagram illustrating the relationship between the contrast difference and the exposure correction value. In FIG. 17, the horizontal axis indicates the contrast difference, and the vertical axis indicates the exposure correction value D_BV_LOCON.
As shown in the graph Hd, the exposure correction value D_BV_LOCON is set to a constant value of 0.375 EV between the contrast differences of 0 to 0.5 EV, but starts to decrease when the contrast difference exceeds 0.5 EV, and the contrast difference becomes smaller. After 1.0 EV, it becomes 0 EV.

  In this way, it is determined whether or not the scene is a low-contrast scene from the entire image, and in the case of low-contrast, shading can be reduced by setting the exposure correction value in the overexposed direction according to the degree. (Described later).

  In step ST56, a correction value related to the control luminance (hereinafter also referred to as “control luminance correction value”) is calculated. Specifically, as in the following equation (5), the maximum value among the exposure correction values D_BV_SKY, D_BV_SNOW, D_BV_MONO, and D_BV_CELL calculated in the above steps ST51 to ST53 and step ST55 is the correction related to the control brightness. Set as the value D_BV_SHD.

D_BV_SHD = Max (D_BV_SKY, D_BV_SNOW,
D_BV_MONO, D_BV_CELL) (5):
In step ST57, the control luminance correction value is adjusted according to the focal length of the taking lens 3. Specifically, the control luminance correction value is corrected according to the focal length fl as in the following cases (i) to (iii).

(i) When fl ≦ 35 mm, D_BV_SHD = D_BV_SHD:
(ii) When 35 <fl ≦ 60 mm, D_BV_SHD = D_BV_SHD × 2/3:
(iii) When 60 mm ≦ fl, D_BV_SHD = D_BV_SHD × 1/3:
By adjusting the correction amount as described above, the control brightness correction amount can be increased on the wide side (telephoto side) where the focal length fl is short and the shading is conspicuous. ) Can suppress the control luminance correction amount.

  In step ST58, the control brightness BVtgt calculated in step ST32 is corrected based on the control brightness correction value adjusted in step ST57. Specifically, the control brightness of the target is set as in the following equation (6).

BVtgt = BVtgt−D_BV_SHD (6):
FIG. 18 is a flowchart corresponding to the above-described step ST7 and showing the control exposure setting operation.

  In step ST61, a control exposure EVtgt is calculated. Specifically, as shown in the following equation (7), the sensitivity value SV corresponding to the ISO sensitivity is subtracted from the control luminance BVtgt obtained in step ST58 to obtain the control exposure EVtgt.

EVtgt = BVtgt-SV (7):
In step ST62, a limit shutter speed TVH for camera shake is calculated. Specifically, the shutter speed TVH at the camera shake limit is calculated in consideration of the focal length fl as in the following equation (8).

TVH = log ₂ (fl) (8):
In step ST63, a limit control exposure EVH with respect to camera shake is calculated. Specifically, as shown in the following equation (9), the sum of the shutter speed TVH at the camera shake limit calculated at step ST62 and the open aperture value AV0 for the diaphragm 302 is set as the control exposure EVH at the camera shake limit.

EVH = TVH + AV0 (9):
In step ST64, the minimum control exposure EVmin is calculated. Specifically, the sum of the shortest (minimum) shutter speed TVmin and the maximum aperture value AV0 is set as the minimum control exposure EVmin as in the following equation (10).

EVmin = TVmin + AV0 (10):
In step ST65, the maximum control exposure EVmax is calculated. Specifically, the sum of the longest (maximum) shutter speed TVmax and the minimum aperture value AVmax related to the aperture 302 is set as the maximum control exposure EVmax as in the following equation (11).

EVmax = TVmax + AVmax (11):
In step ST66, it is determined whether the control exposure EVtgt calculated in step ST61 is smaller than the minimum control exposure EVmin calculated in step ST64. If EVtgt <EVmin, the process proceeds to step ST69. If EVtgt ≧ EVmin, the process proceeds to step ST67.

  In step ST67, it is determined whether the control exposure EVtgt calculated in step ST61 is equal to or greater than the minimum control exposure EVmin calculated in step ST64 and equal to or less than the control exposure EVH of the camera shake limit calculated in step ST63. If EVmin ≦ EVtgt <EVH, the process proceeds to step ST70. Otherwise, the process proceeds to step ST68.

  In step ST68, it is determined whether the control exposure EVtgt calculated in step ST61 is larger than the maximum control exposure EVmax calculated in step ST65. If EVmax <EVtgt, the process proceeds to step ST71. If EVmax ≧ EVtgt, the process proceeds to step ST72.

  In step ST69, the aperture value AV and the shutter speed TV as control values are set as in the following equations (12) to (13).

AV = AV0 (12):
TV = TVmin (13):
In step ST70, an aperture value AV and a shutter speed TV as control values are set as in the following formulas (14) to (15).

AV = AV0 (14):
TV = EVtgt-AV (15):
In step ST71, an aperture value AV and a shutter speed TV as control values are set as in the following formulas (16) to (17).

AV = AVmax (16):
TV = TVmax (17):
In step ST72, an aperture value AV and a shutter speed TV as control values are set as in the following formulas (18) to (19).

AV = Min (AV0 + (EVtgt−EVH) / 2, AVmax) (18):
TV = EVtgt-AV (19):
In step ST73, a control exposure correction value D_EV_SHD considering shading is calculated. Specifically, the control exposure correction value D_EV_SHD is calculated based on the control brightness correction value D_BV_SHD and the like obtained in step ST57 as in the following equation (20).

D_EV_SHD = Min (D_BV_SHD, AVmax−AV) (20):
By calculating such a control exposure correction value D_EV_SHD, a correction amount corresponding to the degree of influence of shading can be obtained.

  In step ST74, the correction amount calculated in step ST73 is reflected in the exposure control, and the aperture value AV and the shutter speed TV related to the aperture 302 are set as in the following equations (21) to (22).

AV = AV + D_EV_SHD (21):
TV = EVtgt-AV (22):
As described above, when the condition of EVH <EVtgt ≦ EVmax is satisfied, that is, when there is a degree of freedom in setting the aperture value and the shutter speed, the aperture value AV is set according to the degree of influence of shading by the above equation (21) By performing the correction (exposure control) set on the narrowing down side, it is possible to reduce the influence of shading on a scene where the influence of shading is large.

  FIG. 19 is a flowchart corresponding to the above-described step ST11 and showing the tone curve selection operation.

  In step ST81, a correction amount DEG_SHADE considering shading is calculated by the following equation (23).

DEG_SHADE = Max (D_BV_SKY, D_BV_SNOW,
D_BV_MONO, D_BV_LOCON) (23):
Note that D_BV_SKY, D_BV_SNOW, D_BV_MONO, and D_BV_LOCON on the right side of the above equation (23) are calculated by performing the same operations as in steps ST5 to ST6 described above based on the photometric / colorimetric information acquired in step ST10. .

  In step ST82, a tone curve for reducing the influence of shading is selected. Specifically, tone curves Fa to Fd are selected according to the correction amount DEG_SHADE calculated in step ST81 based on Table 1 below.

  The four tone curves Fa to Fd selected on the basis of Table 1 convert 12-bit input into 8-bit output as shown in FIG. 20, and medium to high brightness in the order of tone curves Fa, Fb, Fc, Fd. Is set to be processed brighter.

  As described above, since the tone curves Fa to Fd are selected based on the correction amount DEG_SHADE, shading can be appropriately reduced.

  In step ST83, the image correction circuit 124 performs image processing on the image data acquired by the exposure in step ST9 using the one tone curve selected from the four tone curves Fa to Fd in step ST82. Unlike the general shading correction performed by the shading correction circuit 123, this image processing is a process that does not depend on the pixel position related to the image, but such simple processing can quickly reduce shading.

  By the operation of the imaging apparatus 1 described above, since the influence degree of shading is determined based on photometric information and colorimetric information on the peripheral portion of the image, and the action based on the determination result is performed, it is determined whether the scene is easily affected by shading. Can be determined accurately and appropriate measures can be taken. As a result, it is possible to reduce the decrease in the amount of light around the image due to shading.

  In addition, since the imaging apparatus 1 performs over-exposure control for a scene that is easily affected by shading, it is possible to reduce a decrease in peripheral light amount due to shading without using image processing.

  Furthermore, in the conventional shading correction, since the gain at the peripheral portion of the image is forcibly increased by LUT or the like, color noise such as spots may appear in the peripheral portion and the image quality may be deteriorated. Since the tone curve corresponding to the degree of influence is selected, such image quality deterioration can be prevented.

<Modification>
The uniform specific color region detection operation (step ST44 in FIG. 9) in the above embodiment is based on 156 blocks Bk in the image peripheral region EP shown in FIG. 7, and the following equations (1a), (1b) As described above, the standard deviations σ _r and σ _b of each color difference data may be obtained.

In this case, an exposure correction value corresponding to the standard deviations σ _r and σ _b is calculated in step ST55 of FIG. Specifically, an exposure correction value D_BV_LOCON (unit: EV) corresponding to the standard deviations σ _r and σ _b is obtained based on Table 2 below.

  In the operation of step ST56 in FIG. 9 in the above embodiment, the sum of the exposure correction values D_BV_SKY, D_BV_SNOW, D_BV_MONO, and D_BV_CELL may be set as the correction value D_BV_SHD related to luminance.

1 is a diagram illustrating a schematic configuration of an appearance of an imaging apparatus 1 according to an embodiment of the present invention. 1 is a diagram illustrating a schematic configuration of an external appearance of an imaging apparatus 1. FIG. 1 is a diagram illustrating a schematic configuration of an external appearance of an imaging apparatus 1. FIG. 2 is a schematic block diagram illustrating an internal configuration of the imaging apparatus 1. FIG. 3 is a flowchart showing a basic operation of the imaging apparatus 1. It is a flowchart which shows the operation | movement of photometry and colorimetric information acquisition. It is a figure for demonstrating acquisition of the photometry and colorimetric information for every block Bk which divided | segmented the image Go. It is a flowchart which shows the operation | movement of exposure level calculation. It is a flowchart which shows the operation | movement of a scene determination. It is a flowchart which shows the operation | movement of exposure correction | amendment. It is a graph which shows the relationship between a sky blue area | region and an exposure correction value. It is a figure for demonstrating a sky blue area | region. It is a graph which shows the relationship between a high-intensity white area | region and an exposure correction value. It is a figure for demonstrating a high-intensity white area | region. It is a graph which shows the relationship between a uniform specific color area | region and an exposure correction value. It is a figure for demonstrating a uniform specific color area | region. It is a graph which shows the relationship between contrast difference and exposure correction value. It is a flowchart which shows the operation | movement of a control exposure setting. It is a flowchart which shows the operation | movement of tone curve selection. It is a figure which shows four tone curves Fa-Fd.

Explanation of symbols

1 Image pickup device 150 Overall control unit 303 Color image pickup device Bg Grass Bs Sky Bw Snow scene EP Image peripheral area Fa to Fd Tone curve

Claims (13)

An imaging device,
(a) imaging means for acquiring an image relating to the subject;
(b) dividing means for dividing the image into a plurality of regions;
(c) based on photometric information and / or colorimetric information regarding each of the plurality of regions, detection means for detecting the degree of shading related to the image;
(d) means for performing exposure control and / or image processing according to the degree of influence of the shading;
With
The image processing apparatus according to claim 1, wherein the image processing is processing independent of a pixel position related to the image. An imaging device,
(a) imaging means for acquiring an image relating to the subject;
(b) dividing means for dividing the image into a plurality of regions;
(c) photometric means for obtaining photometric information relating to each of the plurality of regions;
(d) colorimetric means for obtaining colorimetric information regarding each of the plurality of regions;
(e) based on the photometric information and / or the colorimetric information, detecting means for detecting the degree of shading related to the image;
(f) a correction amount calculating means for calculating a correction amount according to the degree of influence of the shading;
(g) means for performing exposure control and / or image processing based on the correction amount;
With
The image processing apparatus according to claim 1, wherein the image processing is processing independent of a pixel position related to the image. In the imaging device according to claim 1 or 2,
The colorimetric information is color difference information regarding YCrCb. The imaging apparatus according to any one of claims 1 to 3,
The detection means includes
Means for detecting the degree of influence of the shading based on the sky blue area occupying the periphery of the image;
An imaging device comprising: The imaging apparatus according to any one of claims 1 to 4,
The detection means includes
Means for detecting the degree of influence of the shading based on a high-luminance white area occupying the periphery of the image;
An imaging device comprising: The imaging device according to any one of claims 1 to 5,
The detection means includes
Means for detecting the degree of influence of the shading based on a specific area occupying the periphery of the image;
Have
The imaging device according to claim 1, wherein the specific region is a region of a neighboring color related to a specific color. The imaging apparatus according to any one of claims 1 to 6,
The detection means includes
Means for detecting the degree of influence of the shading based on the difference between the maximum luminance and the minimum luminance in the entire image obtained from the photometric information of each of the plurality of regions;
An imaging device comprising: The imaging device according to claim 2,
In the exposure control, an exposure correction according to the correction amount is performed. The imaging device according to claim 2,
In the exposure control, the image pickup apparatus is characterized in that a correction is performed to set an aperture value on the aperture side in accordance with the correction amount. The imaging device according to claim 2,
(h) selection means for selecting one tone curve from a plurality of tone curves based on the correction amount;
Further comprising
The imaging apparatus according to claim 1, wherein the image processing is image processing using one tone curve selected by the selection unit. The imaging device according to claim 2,
The correction amount calculating means includes
(f-1) adjusting means for adjusting the correction amount according to the focal length of the taking lens;
An imaging device comprising:   A program for causing an imaging device to function as the imaging device according to any one of claims 1 to 11 by being executed by a computer incorporated in the imaging device. A method for performing processing related to shading,
An imaging step of acquiring an image relating to the subject;
A dividing step of dividing the image into a plurality of regions;
A photometric process for generating photometric information for each of the plurality of regions;
A colorimetric process for generating colorimetric information for each of the plurality of regions;
Based on the photometric information and / or the colorimetric information, a detection step of detecting the degree of shading related to the image;
A correction amount calculation step of calculating a correction amount according to the degree of influence of the shading;
A processing step of performing exposure control and / or image processing based on the correction amount;
With
The shading processing method according to claim 1, wherein the image processing is processing independent of a pixel position related to the image.

Images