IMAGE PROCESSING APPARATUS, IMAGE PROCESSING METHOD, AND PROGRAM 5 TECHNICAL FIELD [0001] The invention relates to an image processing apparatus, an image processing method, and a program. In particular, the invention relates to an image processing apparatus, an 10 image processing method, and a program that performs signal processing on an output of a single plate-type image sensor, BACKGROUND ART [0002] 15 When a single plate-type solid-state image sensor is used as an image sensor of an imaging apparatus, only a single spectral sensitivity is obtained. Therefore, generally, color imaging is performed by arranging color filters of different colors such as R, G, and B on image sensors 20 corresponding to respective pixels. In this method, only one color (for example, any one of R, G, and B) is obtained with each pixel. Accordingly, a mosaic-like image based on color is generated. [0003] 25 Specifically, only color information, R or G or B or the like, is acquired for each pixel according to the pattern of filters. This image is called a so-called mosaic image. In order to obtain a color image from the mosaic image, it is necessary to obtain the color information of every color 30 for each of all the pixels. [0004] 1 SP263074WO00 A color image can be generated by calculating color information of all colors (for example, all the RGB) corresponding to each of all pixels by interpolating color information obtained from surrounding pixels of each pixel. 5 This interpolation processing is called demosaic processing. [0005] For example, an example of the color filters used for an imaging apparatus is illustrated in Fig. 1(1). This array is calledBayer pattern, and transmiIts light (R, G, or B) having 10 a specific wavelength component in units of a pixel. In the Bayer pattern, a minimum unit consists of four pixels which include two filters to transmit a green (G), one filter to transmit a blue (B), and one filter to transmit a red (R). [0006] 15 With the miniaturization of the image sensor, the sensor becomes easily affected by a minute difference in pixel structure. Therefore, it becomes apparent that even the pixels having the same spectral characteristic (for example, G pixels in the Bayer pattern) are different in sensitivity 20 from pixel to pixel due to the slight difference in the structure. [0007] For example, as illustrated in Fig. 1(2), the G pixels include G pixels in an R line (hereinafter, referred to as 25 Gr pixels) and G pixels in a B line (hereinafter, referred to as Gb pixels) . Although the Grpixels have G filters having the same spectral characteristic as those of the Gb pixels, there might be sensitivity differences because of the slight structural differences. 30 [000£3] When the above--mentioned demosaic processing is 2 SP263074WO00 performed on an image imaged by the image sensors having the sensitivity differences, a portion having small differences in brightness, which may be originally determined to be a flat portion, is erroneously determined to be an edge portion due 5 to the difference in DC component between the Gb pixels and the Gr pixels. As a result, an error occurs in selecting surrounding pixels used to determine a pixel value of a specific pixel, so that a plurality of interpolation values is mixed irregularly. This is likely to result in generation of an 10 artifact that stands outverymuche Therefore, it is necessary to perform correction processing on the sensitivity difference before the demosaic processing is performed. The demosaic processing is described, for example, in Patent Document 1 (Japanese Patent No. 2931520)° 15 [0009] When the sensitivity differences have the same tendency over the entire screen, the correction may be performed by adjusting the level and/or the offset. That is, since the correction is performed such that the sensitivity of the G 20 pixels in a R line (Gr pixels) matches the sensitivity of the Gpixels in a B Line (Gb pixels) , the following can be estimated with use of coefficients A and Be [0010] [Formula 1] 25 Gb= GrxA+B ...(Expression 1) [0011] In the above expression (Expression 1) , data that shows a bar above Gb indicates a pixel value obtained by correcting 30 the sensitivity of the G pixels in an R Line (Gr pixels) so 3 SP263074WO00 as to match the sensitivity of the Gb pixels. The symbol "-" (bar) written above Gb or the like in expressions is written in the form of Gb(-) in the specification. [0012] 5 When the sensitivity differences have the same tendency over the entire screen, it is effective to use a correction value obtained by using the above expression (Expression 1). However, causes of generation of the sensitivity differences at the positions of respective pixels include various factors 10 such as a pixel structure and an angle of incident light. Therefore, the sensitivity varies from pixel to pixel (for example, an upper side and a lower side of a screen) e Moreover, even the same pixel changes in sensitivity due to the influence of the aperture of a lens or the like. 15 [0013] A method of absorbing the level difference according to the pixel position is also proposed, The method measures the difference in the sensitivity of each area, and absorbs the sensitivity difference by performing the correction 20 processing based on the gain and the offset, For example, when a horizontal distance from the center is assumed Lo be x and a vertical distance is assumed to be y, a correction coefficient for each pixel can be approximately calculated by using a correction function f (x, y) and a correction function 25 g(x, y) calculated from the sensitivity difference of each area, and the correction can be performed as follows. [0014] [Formula 2] Gb Grxf(x,y)+ g(x,y) 30 ...(Expression 2) 4 SP263074W000 [0015] However, this method achieves only a rough correction for each area. Accordingly, the sensitivity difference between fine areas cannot be absorbed. In addition, since 5 the sensitivity also depends on optical characteristics such as an aperture and a zoom state of a lens, a great deal of labor and time is required to measure the f(x, y) and/or the g (x, Y) [0016] 10 There is also a technique to absorb the sensitivity difference by using only information on adjacent pixels. In Patent Document 2 (Japanese Patent Application Laid-open (JP-A) No. 2005-160044), image processing is performed when performing the demosaic processing on an image of four colors 15 obtained by using a color filter for transmitting an emerald (E) in addition to filters for transmitting R, G, and B as illustrated in Fig. 1(3) by using the fact that spectral characteristics of color filters of G and E are similar to each other. By estimating E pixels at the positions ofG pixels 20 and estimating G pixels at the positions of E pixels, an image illustrated in Fig. 1(4) can be produced. [0017] For the image arrayed as illustrated in Fig. 1(4), it becomes possible to perform demosaic processing similar to 25 the demosaic processing which is applied to the Bayer pattern (Fig. 1(1)). However, although the spectral characteristics and/or the sensitivities of the G filter and the E filter are different as illustrated in Fig. 2, since the spectral characteristics thereof partially overlap, there is a strong 30 correlation between the G pixel and the E pixel. Accordingly, estimation of regression analysis can be used to estimate the 5 SP263074WO00 E pixels at the positions of the G pixels or to estimate the G pixels at the positions of the E pixels. [0018] The technique which estimates G pixels at the positions 5 of E pixels is illustrated as an example. The weighted mean mE and mG of adjacent E pixels is calculated as follows. [0019] [Formula 3] mE 10 ...(Expression 3) ...(Expression 4) [0020] In the above expressions (Expression 3) and (Expression 15 4) , i represents a pixel number of a certain surrounding pixel, Ei represents a pixel value of an E pixel correspondi..riq to the number, and Ci represents a weighting factor corresponding to the distance from a center pixel. j represents a pixel number of another certain surrounding pixel, Gj represents 20 a pixel value of a G pixel corresponding to the number, and Cj represents a weighting factor corresponding to the distance from the center pixel. [0021] Dispersion VGG of the adjacent G pixels and covariance 25 VEG of the G pixels and the E pixels are calculated considering the difference in the spectral characteristic between the E 6 SP263074W000 pixel and the G pixel illustrated in Fig. 2, and an estimation value of the E pixel is estimated as follows. [0022] [Formula 4] 5 KEG x (G - mG) + mE VGG ...(Expression 5) [0023] In the above-mentioned (Expression 5) , it is necessary to perform calculations of the dispersion and the covariance, 10 and the calculation amount of these operations is very large. Accordingly, in some cases, such estimation is practically performed by using an operation lighter than (Expression 5) as described below. [0024] 15 [Formula 5] mG ...(Expression 6) [0025] However, it is also understood that this expression 20 (Expression 6) requires multiplication and division operations. Furthermore, it is understood that, when it is achieved with a circuit, it costs a lot. [0026] The technique disclosed in Patent Document 2 (JP-A No. 25 2005-160044) can be used not only to perform processing on R, G, B,, and E illustrated in Fig. 1(4) but also to perform correction by estimating the sensitivity difference between 7 SP263074WO00 the Gb pixel and the Gr pixel in the Bayer pattern illustrated in Fig. 1(2). However, a great amount of calculations is necessary to calculate the dispersion and the covariance in the above-mentioned (Expression 5), and an amount of 5 calculation is also large in a simpler expression (Expression 6) because it includes divisions. [0027] The spectral characteristics of the G filter and the E filter are different as illustrated in Fig. 2 in the (use 10 ofthearrayofR, G, B, andEillustratedinFi:g. 1(4) . However, in the Bayer pattern illustrated in Fig. 1 (2) , although the filter characteristics of the Gb filter and the Gr filter are affectedby color mixture, pixel structure, and incident light, the filter characteristics are very similar to each other as 15 illustrated in Fig. 3. Therefore, it is anticipated that there is a correlation between them which is stronger than the correlation between the G pixel and the E pixel, and the correction can be achieved with a smaller amount of operations. 20 CITATION LIST PATENT DOCUMENTS [0028] Patent Document 1: Japanese Patent No. 2931520 Patent Document 2: Japanese Patent Application Laid-Open No. 25 2005-160044 SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION [0029] 30 The invention is made in view of the above problems and is intended to provide an image processing apparatus, an image 8 SP2630 74WO00 processing method, and a program which can perform correction processing on a mosaic image imaged by using a specific color filter for a single plate-type image sensor with a smaller amount of operations and with high accuracy and which achieves 5 a high-quality color image. SOLUTIONS TO PROBLEMS [0030] A first aspect of the present invention is an image 10 processing apparatus including: a sensitivity difference correction processing unit that receives a photoelectric conversion signal and executes sensitivity difference correction processing, the photoelectric conversion signal being output by an image sensor 15 based on incident light being incident through a color filter, wherein the sensitivity difference positive processing unit: acquires a pixel value of a color filter unit which has a same color as a correction target pixel and is present in surroundings of the correction target pixel; calculates an 20 additional value by adding a difference between weighted mean pixel values "a" and "b" of two kinds of pixel groups "A" and "B" classified according to positions of the pixels to the pixel value of the correction target pixel, the weighted mean pixel values corresponding to distances of the pixel groups 25 from the correction target pixel; and calculates a mean value of the pixel value of the correction target pixel and the additional value as a corrected pixel value of the correction target pixel. [0031] 30 Furthermore, according to an embodiment of the image processing apparatus of the presentinvent_ion,thecolorfilter 9 S2263074WO00 is arrayed in a Bayer pattern, and the sensitivity difference correction processing unit has a configuration which a sensitivity difference between an Gr pixel and a Gb pixel included in an image which is imaged through the color filter 5 of the Bayer pattern is corrected. [0032] Furthermore, according to an embodiment of the image processing apparatus of the present invention, the sensitivity difference correction processing unit: calculates, when 10 performing correction processing on the Gr pixel and the Gb pixel, weighted pixel value means mGr and mGb corresponding to distances of the Gr pixel and the Gb pixel, which are adjacent to the correction target pixel, from the correction target pixel; calculates an additional value by adding a difference 15 between the mGr and the mGb to the pixel value of the correction target pixel; and calculates the mean value of the pixel value of the correction target pixel and the additional value as the corrected pixel value of the correction target pixel. [0033] 20 Furthermore, according to an embodiment of the image processing apparatus of the present invention, thesensit.ivity difference correction processing unit: calculates a final corrected pixel value by reducing a contribution level of the additional value when an adjacent image area including the 25 correction target pixelis an edge area; and calculates the final corrected pixel value by increasing the contribution level of the additional value when the adjacent image area including the correction target pixel is a flat area, [0034] 30 Furthermore, according to an embodiment of the image processing apparatus of the present invention, the sensitivity 10 SP263074W000 difference correction processing unit has a configuration in which demosaic processing is executed. [0035] Furthermore, according to an embodiment of the image 5 processing apparatus of the present invention, the sensitivity difference correction processing unit has a configuration in which demosaic processing of determining a pixel value of a processing target pixel is performed based on a pixel value of a reference pixel by determining the contribution level 10 of the pixel value of the reference pixel adjacent to the processing target pixel according to a result of the edge direction determination of an image area including the processing target pixel of the demosaic processing. [0036] 15 Furthermore, according to an embodiment of the image processing apparatus of the present invention, the sensitivity difference correction processing unit has a configuration in which demosaic processing of determining the pixel value of the processing target pixel is performed by setting the 20 contribution level of the pixel value of the reference pixel in a direction where a change in pixel value is small to a high level, according to a result of the edge direction determination of the image area includi.ngtheprocessing target pixel of the demosaic processing. 25 [0037] A second aspect of the present invention is an image processing apparatus including: an imaging device; and the sensitivity difference correction processing unit. 30 [0038] ' A third aspect of the present invention is an image 11 SP263074WO00 processing method executed in an image processing apparatus, the method including: by asensitivity difference correction processing unit, receiving a photoelectric conversion signal that is output 5 by an image sensor based on incident light being incident through a color filter, and executing sensitivity difference correction processing, wherein the sensitivity difference positive processing executes e acquiring a pixel value of a color filter unit wh:i_ch 10 has a same color as a correction target pixel and is present in surroundings of the correction target pixel; calculating an additional value by adding a difference between weighted mean pixel values "a" and "b" of two kinds of pixel groups "A" and "B" classified according to positions of pixels, the 15 weighted pixel value means corresponding to distances of the pixel groups from the correction target pixel, to a pixel value of the correction target pixel; and calculating a mean value of the pixel value of the correction target pixel and the additional value as a corrected pixel value of the correction 20 target pixel. [0039] A fourth aspect of the present invention is an program that causes image processing to be executed in an image processing apparatus and causes a sensitivity difference 25 correction processing unit to receive a photoelectric conversion signal that is output by an image sensor based on incident light being incident through a color filter, and to execute sensitivity difference correction processing, wherein 30 the sensitivity difference positive processing executes acquiring a pixel. value of a color filter unit which 12 SP263074WO00 has a same color as a correction target pixel and is present in surroundings of the correction target pixel; calculating an additional value by adding a difference between weighted mean pixel values "a" and "b" of two kinds of pixel groups 5 "A" and "B" classified according to positions of pixels, the weighted pixel value means corresponding to distances of the pixel groups from the correction target pixel, to a pixel value of the correction target pixel; and calculating a mean value of the pixel value of the correction target pixel- and the 10 additional value as a corrected pixel value of the correction target pixel. [0040] The program of the invention is, for example, a program that can be provided by a communication medium or a recording 15 medium which is provided, for example, to an image processing apparatus or a computer system, which can execute various program codes, in a computer-readable format. By providing such a program in a computer-readable format, the processing performed according to the program can be implemented in the 20 image processing apparatus or the computer system. [0041] Other objects, features, and advantages of the invention will become apparent in light of a more detailed description based on embodiments of the invention to be described later 25 and the attached drawings. The term "system" in this specification means a configuration of a logical set of a plurality of devices, and each device in the configuration is not necessarily provided in the same casing. 30 EFFECTS'OF THE INVENTION [0042] 13 SP263074WO00 According to a configuration of one embodiment of the invention, provided are an apparatus and a method that execute sensitivity correction processing of an image signal generated by a single plate-type image sensor through a color filter. 5 Specifically, the sensitivity difference correction of Grand Gb signals included in an image signal, for example, an RGB signal, generated by a single plate-type image sensor through a color filter. Pixel values of color filter units having a color the same as that of a correction target pixel and hei.ng 10 provided around the correction target pixel are acquired. A difference between weighted mean pixel values "a" and "b" of two kinds of pixel groups "A" and "B" classified according to positions of pixels is added tot pixel value of the correction target pixel to calculate an additional value in which the 15 weighted mean pixel values are based on the distance from the correction target pixel. A mean value of the pixel value of the correction target pixel and the additional value is calculated as a corrected pixel value of the correction interest pixel. According to this processing, the correction 20 processing can be performed with a simple operation and with high accuracy.. BRIEF DESCRIPTION OF DRAWINGS [0043] 25 Fig. 1 is a diagram that describes a Bayer pattern, which is a color array, used for general color filters, and a problem thereof. Fig. 2 is a diagram that describes spectral characteristics and sensitivities of a G filter and an E filter . 30 Fig. 3 is a diagram that describes filter characteristics of a Gb filter and a Gr filter. 14 SP263074WO00 Fig, 15 is a diagram that describes a configuration example of a correlation processing unit 149 in the sensitivity difference correction and demosaic processing unit 131 of the DSP block 103 in the sixth embodiment. 5 Fig. 16 is a diagram that describes processing executed by a G high frequency generating unit 151 of the correlation processing unit 149. Fig. 17 is a diagram that describes the sensitivity difference correction and demosaic processing unit 131 in a 10 seventh embodiment, Fig, 18 is a diagram that describes an example of an advantage obtained by the processing of the invention. Fig. 19 is a diagram that describes a configuration example of hardware of the image processing apparatus of the 15 invention. MODE FOR CARRYING OUT THE INVENTION [0044] Hereafter, an image processing apparatus, an image 20 processing method, anda program of the invention are described with reference to the drawings. A description is made :iri the following order: 1, Regarding a configuration of an image processing apparatus and sensitivity difference correction processing 25 according to a first embodiment of the invention; 2. Regarding an example of sensitivity difference correction processing in which an edge portion is considered (second embodiment); 3. Regarding an example of sensitivity difference 30 correction processing in which an edge portion is considered (third embodiment); 16 SP263074W000 4. Regarding an example of sensitivity difference correction processing in which an edge portion is considered (fourth embodiment); 5. Regarding an example of sensitivity difference 5 correction processing in which an edge portion is considered (fifth embodiment); 6. Regarding an embodiment (sixth embodiment) in which sensitivity difference correction processing and demosaic processing are combined; 10 7. Regarding an embodiment (seventh embodiment) i_n which sensitivity. difference correction processing and demosaic processing are combined; and B . Regarding a hardware configuration example of an image processing apparatus. 15 [0045] 1. Regarding a configuration of an image processing apparatus and sensitivity difference correction processing according to a first embodiment of the invention A configuration example of an image processing apparatus 20 of the invention is described with reference to Fig. 4. Fig. 4 is a block diagram that illustrates an example of a configuration of an imaging apparatus that is one embodiment of the image processing apparatus of the invention. The image processing apparatus of the invention may be an apparatus that 25 can execute demosaic processing by receiving a mosaic image imagedby using a specific color filter for a single plate-type image sensor. The image processing apparatus of the invention is not limited to an imaging apparatus and can be implemented by a device such as a PC. Hereinbelow, an example of an imaging 30 apparatus is described as an example of the image processing apparatus of the invention, 17 SP263074WO00 [0046] In an imaging apparatus 100 illustrated in Fig. 4, light incident through an optical lens 101 is incident on an imaging device 102 configured by a CCD, a CMOS image sensor, or the 5 like. The imaging device 102 generates image data (a photoelectric conversion signal), based on the light, which is input to a single plate-type image sensor through a color filter, and inputs the image data to a DSP block 103. [0047] 10 The image data (the photoelectric conversion signal) is input to the DSP block 103, and is then subjected to signal processing for an output signal here, As a result, output image 104 is output. [0048] 15 An example of the configuration of the DSP block 103 is described with reference to Fig, 5. An image of the Bayer pattern illustrated in Fig. 1(1) is output from the imaging device 102 illustrated in Fig. 4 and is input to the DSP block 103. However, this input data has the sensitivity differences 20 according to the positions of G. That is, the input data becomes mosaic data that corresponds to the array (R, Gb, Or, B) illustrated in Fig, 1 (2) . The positions of Gb and Gr pixels are positions where the same G fillers are set. However, since the positions are different, they are sensitive to beams of 25 slightly different wavelengths. That is, they have a sensitivity difference. [0049] In a sensitivity difference correction processing unit 111 of the DSP block 103, the sensitivity difference between 30 the Or pixel and the Gb pixel which has the same optical characteristic in the Bayer pattern illustrated in Fig, 1(2) 18 SP263074W000 is corrected and an image of the Bayer pattern (RGB) illustrated in Fig. 1(1) is output. That is, a photoelectric conversion signal generated based on the light input to the single plate-type image sensor through the color filter is input and 5 sensitivity difference correction processing is executed. [0050] In a white balance processing unit 112, pixel values of R, G, andBchannels inanachromaticcolor area aremultiplied by appropriate coefficients corresponding to respective 10 colors so that the pixel values may become equal to each other, and a white balance-adjusted image is output. A demosaic processing unit 113 executes demosaic processing that sets all RGB pixel values for each pixel position, with respect to a mosaic image where only one pixel value out of information 15 of the RGB pixel values is set for each pixel position. Specifically, it performs equalization processing of providing each pixel position with three channels of R, G, and B by using pixel value information of adjacent pixels and outputs the resultant. 20 [0051] In a gamma correcting unit 114, nonlinear correction processing is performed so that the brightness and the color saturation of the image, which is output as an output image 104 illustrated in Fig. 4, can be correctly displayed and the 25 corrected image is output. A YC converting unit 115 genera Les and outputs an Y image and a C image by performing matrix conversion processing on the input three-channel image (image with R, G, B channels) and performing processing of limiting bandwidths of chromatic components. 30 [0052] Details of the sensitivity difference correction 19 SP263074WO00 processing unit 111 are described with reference to Fig. 6. Fig. 6 is a diagram that illustrates an example of a detailed configuration of the sensitivity difference correction processing unit 111 (see Fig. 5) of the DSP block 103 of the 5 image processing apparatus 100 of the invention illustrated in Fig. 5. [0053] A GL mean value calculating unit 121 is a block to undergo a weighted mean of the pixel values of adjacent Or pixels of 10 an interest pixel. The interest pixel is a pixel to be subjected to.pixel-value correction and setting processing. For all the pixels which form the image, the pixels are sequentially selected one by one and the processing is performed. When the weighted mean of Or is assumed to be mGr, 15 the Gr mean value calculating unit 121 calculates the mGr based on the following expression (Expression 7). [0054] [Formula 6] (Gr' x C1 ) mGr 20 ...(Expression 7) [0055] The weighted mean of Or, mGr, can be calculated by the above-mentioned (Expression 7). In the above expression (Expression 7), i represents a pixel number of a certain 25 surrounding pixel, Gri represents a pixel value of the Or pixel corresponding to the pixel number i, and Ci represents a weighting factor corresponding to the distance from a center pixel. 20 SP263074WO00 [0056] A Gbmean value calculating unit 122 is a block to undergo a weighted mean of the pixel values of the Gb adjacent to the interest pixel. When a weighted mean of the Gb is assumed 5 to be mGb, the mGb can be calculated based on the following expression (Expression 8). [0057] [Formula 7] 10 ..(Expression 8) [0058] In the above expression (Expression 8), j represents a pixel number of a certain surrounding pixel, Gbj represents a pixel value of the Gb pixel corresponding to the pixel number 15 j, and Cj represents a weighting factor corresponding to the distance from the center pixel. [0059] In a sensitivity difference correcting unit 123, the sensitivity difference of the interest pixel is corrected by 20 using the Gb or the Gr which is the interest pixel, the weighted mean mGr of the Gr obtained by the Gr mean value calculating unit 121, and the weighted mean mGb of the Gb obtained by the Gb mean value calculating unit 122. [0060] 25 As illustrated in Fig. 7, a mean value of sensitivity-corrected Gb and Gr is calculated and output to the positions of the Gbpixels and the Gr pixels by the correction processing.. 21 SP263074TRO00 [0061] A method of calculating estimation values of the Gb pixels and theGrpixels isshown here. As previously described with reference to Fig. 3, the characteristics of the Gb filter 5 and the Gr filter are the same, and only the sensitivities thereof are slightly different due to the influence of the pixel structure and the incident light. Therefore, the image can be sufficiently corrected by removing the sensitivity difference at a low frequency by using the weighted mean mGr 10 of the adjacent Gr pixels and the weighted mean mGb of the Gb pixels. [0062] When a Gb pixel is the interest pixel as a correction target, it is necessary to estimate a value of the Gr pixel 15 at the position of the interest pixel. The value of the Gr pixel at the position of the interest pixel Gb means the pixel value when the Gb pixel, which is the interest pixel, has the same sensitivity as the Gr pixel being present in the surroundings. The estimation value Cr (-) of the Gr pixel 20 at the position of the interest pixel can be calculated as follows. In addition, as described above, the symbol"-(bar)" above Gr or the like in expressions is written in the form of Gr(-) in the specification. [0063] 25 [Formula 8] Gr_ Gb + (rGY--mOb) a.e(Expression 9) [0064] In the above-mentioned (Expression 9), Gb is the pixel 30 value of the interest pixel, and mGr and mGb are the weighted 22 SP263074WO00 mean values of Gr and Gb adjacent to the interest pixel which are calculated based on the previously described (Expression 7) and (Expression 8). [0065] 5 When the Gr pixel is an interest pixel as a correction processing target, it is necessary to estimate the Gb pixel at the position of the interest pixel. The value of the Gb pixel at the position of the interest Gr pixel means a pixel value when the Gr pixel, which is an interest pixel, has the 10 same sensitivity as the surrounding Gb pixel. Estimation value Gb (-) of the Gb pixel at the position of the interest pixel can be calculated as follows, [0066] [Formula 9] 15 Gb = Gr + (;mGb - mnGr) e.a (Expression 10) [0067] In the above-mentioned (Expression 10) , Gr is the pixel value of the interest pixel, mGr and mGb are the weighted 20 mean values of Cr and Gb adjacent to the interest pixel which are calculated based on the previously described (Expression 7) and (Expression 8).. [0068] By using the above-mentioned (Expression 9) and 25 (Expression 10), as illustrated in Fig. 7, sensitivity-corrected G pixel values can be set for the positions of all the G pixels (original Gb and Gr). The sensitivity-corrected G pixel value (G(-)) is calculated as follows e When a Gb pixel is the interest pixel as a correction 30 target, the pixel value of the interest pixel becomes an 23 SP263074WO00 arithmetic mean value of the original pixel value of the Gb pixel and the estimation value Gr (-) of the Gr pixel calculated by the above-mentioned (Expression 9). When a Gr pixel is the interest pixel as a correction target, the pixel value 5 of the interest pixel becomes an arithmetic mean value of the original pixel value of the Gr pixel and the estimation value Gb(-) of the Gb pixel calculated by the above-mentioned (Expression 10). [0069] 10 A specific expression is shown below. When the interest pixel is Gb, a G pixel value G(-) which has undergone the sensitivity difference correction is calculated by the following (Expression 11).. [0070] 15 [Formula 10] Cb+Gr_Gb+G 2 ...(Expression 11) [0071] -- nGb 2 Moreover, when the interest pixel is Gr, a G pixel value 20 G(-)which has undergone the sens itivity difference correction is calculated by the following (Expression 12). [0072] [Formula 11] Gb + Gr nGb -- mGrr -Gr+ 25 ...(Expression 12) [0073] - 2 In the invention, the corrected C pixel value 24 SP263074W000 corresponding to the position of the Gb pixel or the Gr pixel which is obtained by a single-plate type image sensor is calculated by using the above-described expressions, that is, from (Expression 7) to (Expression 12). 5 [0074] As understood by referring to the above-mentioned (Expression 7) to (Expression 12), the operations of (Expression 7) to (Expression 12) can be executed only by additions and subtractions. Ci and Cj that are denominators 10 in (Expression 7) and (Expression 8) are coefficients corresponding to the distances from the interest pixel and can be freely set, Therefore, the value of the denominator in (Expression 7) and (Expression 8), which is the sum of Ci and Cj, can be freely set. When it is set to the square of 15 the sum, the division can be achieved only by bit shifting, Since the divisions in (Expression 11) and (Expression 12) can be achieved by the bit shifting, all the expressions from (Expression 7) to (Expression 12) can be achieved only by additions andsubtractions. Therefore, a configuration which 20 calculates the value of the corrected G pixel at the position of the Gr pixel or the Gb pixel with a far lighter opera Lion than conventional methods which use the previously described (Expression 5) and (Expression 6) can be achieved. [0075] 25 2. Regarding an example of sensitivity difference correction processing in which an edge portion is considered (second embodiment) Next, an example of sensitivity difference correction processing in which an edge is considered is described as a 30 second embodiment of the image processing apparatus of the invention. 25 S2263074WO00 [0076] As described above, in the image processing apparatus of the invention, the sensitivity difference correction can be performed by using an operation process to which the 5 previously described (Expression 7) to (Expression 12) are applied. In an image generated by the demosaic processing or the like performed based on the G pixel obtained by the correction processing, the artifact especially in the flat portion disappears so that a fairly good output image is 10 obtained in many cases, [0077] However, this correcti_oonnprocessing is alaccompanied by an aspect in which frequency characteristic in the vicinity of the Nyquist frequency is deteriorated. A case where an 15 image signal having a monochrome edge of a vertical stripe as illustrated in fig. 8 is input will be described as an example, [0078] When the G pixel values, which have undergone the sensitivity correction using the previously described 20 (Expression 11) and (Expression 12), are set with respect to the image signal , having a monochrome edge of a vertical sL.ripe illustrated in Fig. 8, both of the Gb pixel and the Gr pixel have an intermediate value between a value of white and a value of black, that is, gray. As the result of correction, the 25 G pixels become a flat image, That is, the above-described correction processing is likely to result in blurry edges. [0079] Hereafter, an embodiment to prevent blurry edges is described as a second embodiment, An image processing 30 apparatus of the second embodiment has the configuration which has been described referring to Figs. 4 to 6 like in first 26 SP263074WO00 embodiment. However, in the present embodiment, an expression obtained by modifying arithmetic expressions (Expression 11 and Expression 12) which calculate the pixel values of the G pixels, G(-), which have undergone the 5 sensitivity difference correction in first embodiment is used to calculate corrected pixel values of the G pixels. [0080] In the second embodiment, when an interest pixel is Gb, the G pixel value G(-) which has undergone the sensitivity 10 difference correction is calculated by replacing (Expression 11) which has been described in the first embodiment with the following (Expression 13) or (Expression 15) to be described below, and by applying (Expression 13) or (Expression 15). Moreover, when the interest pixel is Gr, the G pixel value 15 G(-) which has undergone the sensitivity correction is calculated by replacing (Expression 12) which has been described in the first embodiment with the following (Expression 14) or (Expression 16) to be described below, and by applying (Expression 14) or. (Expression 16). 20 [0081] [Formula 12] G =Gb+ax rnGr - mGb 1 2 e.. (Expression 13) G =Gr+ a x (rGb -- mGr) L' 25 ...(Expression 14) [0082] In the above -mentioned ( Expression 13) and ( Expression 27 SP263074WO00 14), a is a coefficient which indicates a correction effect, and is in the range of 0 5 a < 1. When the coefficient a is set to a small value, the influence of the subsequent terms ofaintheexpression isless, and the correctioneffectbecomes 5 weak. Accordingly, the edge characteristic may remain. On the other hand, when the coefficient is set to a large value, the correction effect becomes strong, As a result, the artifact in the flat portion does not stand out. [0083] 10 In the correction of the pixel value, it is difficult to reduce only the artifact with the edge characteristic being maintained. That is, the artifact in the flat portion and the edge characteristic are in the trade--off relationship, so that it is difficult to achieve both the correction of the 15 artifact in the flat portion and the maintaining of the edge portion at the same time. [0084] However, if adaptive processing is performed in which the coefficient a in the above-mentioned (Expression 13) and 20 (Expression 14) is set to 0 or a value near 0 for the edge portion and the coefficient a is set to 1 or a value near 1 for the flat portion, it is possible to correct the artifact of the flat portion while maintaining the edge portion. [0085] 25 In addition, in order to achieve the correction of the artifact of the flat portion with the edge portion maintained, the above-mentioned. (Expression 13) and (Expression 14) are replaced with the following (Expression 15) and (Expression 16). 30 [0086] When the interest pixel is Gb, the G pixel value G(-) 28 SP263074WO00 which has undergone the sensitivity difference correction is calculated by using the following (Expression 15). Moreover, when the interest pixel is Gr, the G pixel value G(-) which has undergone the sensitivity difference correction is 5 calculated by using the following (Expression 16). [0087] [Formula 13] d= Gb+ f(mt r --mcb)x ImGr-- mdTb 2 2 10 -(Expression 15) U 13 -(Expression 16) [0088] (mGb -mGr mGb- rGr) 9 2 J (Expression 15) and (Expression 16) correspond to the expressions obtained by substituting the coefficient a in the 15 previously described (Expression 13) and (Expression 14) as follows. a = (3((mGr - mGb)/2), or a = (3((mGb - mGr)/2) A function (3(-) in the above-mentioned (Expression 15) 20 and (Expression 16) is a function defined by following (Expression 17) [0089] [Formula 14] I.xkTH otherwise 25 .. e. (Expression 17) 29 SP263074W000 above-mentioned (Expression 15) and (Expression 16) by using the weighted mean mGr of Gr obtained by the Gr mean value calculating unit 121, the weighted mean mGb of Gb obtained by the Gb mean value calculating unit 122, and the interest 5 pixel Gb or Gr. [0094] The effect of the corrected G pixel value, which is calculated according to the above-mentioned (Expression 15) and (Expression 16) used in second embodiment, is described 10 by using an image illustrated in Fig. B. The image illustrated in Fig. 8 is an image where the pixel value of the Gb pixel is low and the pixel value of the Gr pixel is high. [0095] Therefore, a difference between the weighted mean mGr 15 of Gr, which is calculated by the Gr mean value calculating unit 121 according to the above-mentioned (Expression 7), and the weighted mean mGb of Gb which is calculated by the Gb mean value calculating unit 122 according to the above-mentioned (Expression 8), that is, a difference between the mGr and the 20 mGb is increased. [0096] Therefore, as for Q ((mGr - mGb) /2) / 2 ) in (Expression 15) and (Expression 16) , in these expressions, the absolute values of ((mGr - mGb)/2) and ((mGb - mGr)/2), 25 are increased. [0097] That is, the followings are set: ((mGr - mGb)/2) > TH and ((mGb - mGr)/2) < -TH or, 30 ((mGr - mGb)/2) < -TH and ((mGb - mGr)/2)> TH [0098] 31 SP263074WO00 As a result, as shown in the previously described expression (Expression 17) and as illustrated in Fig. 9(1), the values of (3((mGr - mGb)/2) and (3((mGb - mGr)/2) become 0. 5 [0099] Thus, (3(x) becomes 0, and, as a result, the value of the latter half (subsequent to (3) of the previously described (Expression 15) and (Expression 16) becomes 0, and the sensitivity difference correction processing will not he 10 performed. With this processing, the pixel value of the edge portion is output as it is, so that an event in which the edge is blurred does not occur. [0100] On the other hand, when a processing target image portion 15 portion is not an edge portion but a flat portion, a difference between the weighted mean mGr of Gr and the weighted mean mGb of Gb which are calculated by the previously described (Expression 7) and (Expression 8), that is, a difference between the mGr and the mGb is equal in value to the sensitivity 20 difference which is desired to be corrected. The maximum amount to be corrected is set to a threshold TH in the above-mentioned (Expression 17) considering the. image sensor and the optical characteristic. [0101] 25 That is, in connection with Q ((mGr - mGb) /2) and p ((mGb - mGr)/2) in the above-mentioned (Expression 15) and (Expression 16), in these expressions, , by using the values (absolute values) of ( (mGr - mGb) /2) and ( (mGb - mGr) /2) , the threshold (TH), which is the reference to separate the flat 30 portion as a correction target and the edge portion which is not the correction target from each other, is seta 32 SP263074W000 [0102] With such a setting, when ( (mGr - mOb) /2) > TH and ( (mGb - mGr)/2) < -TH, or when ((mGr mGb) /2) < - TH and ((mGb - mGr)/2) > IN, that is, when the followings are set, such a 5 portion is determined to be an edge portion. Moreover, as shown in the previously described expression (Expression 17) and illustrated in Fig. 9(1),the values of ((mGr - mGb) /2) and (3 ( (mGb - mGr) /2) become 0, and the latter half (subsequent to in the previously described (Expression 15) and 10 (Expression 16) becomes 0. Accordingly, the sensitivity difference correction processing will not be performed. [0103] On the other hand, as for ( (mGr - mGb) /2) > TH and ( (mGb - mGr) /2) < -TH, or ( (mGr - mGb) /2) < -TH and ( (mGb - mGr) /2) 15 > TH, in the cases other than the above settings, the portion is determined to be a flat portion. As a result, as shown in the previously described (Expression 17) and as illustrated in Fig. 9 (1) , the values of 0 ( (mGr -mGb) /2) and P ( (mGb -mGr) /2 ) become 1, and the latter half (subsequent to a) in the previously 20 described (Expression 15) and (Expression 16) becomes a value other than 0. That is, the sensitivity difference cor.rec Lion processing will be performed. In this case, the processing for the flat portion becomes the processing equivalent to (Expression 11) and (Expression 12) in the embodiments, and 25 the artifact that stands out in the flat portion due to the sensitivity difference can be corrected. [0104] 3. Regarding an example of sensitivity difference correction processing in which an edge portion is considered 30 (third embodiment) Next, an example of sensitivity difference correction 3 3 SP263074W000 processing in which an edge portion is considered like the second embodiment is described as a third embodiment of an image processing apparatus of the invention, [0105] 5 The third embodiment is an embodiment obtained by changing the function (1(x) which has been described with reference to (Expression 17) and Fig. 9(1) in the above-mentioned second embodiment. [0106] 10 In the third embodiment, the function D(x) is set as illustrated in Fig, 9(2). That is, (3(x) = 1 at -TH1 < x < TH1, (3(x) = 0 at x < -TH2 or TH2 <_ x, (3(x) linearly changes in the range of 0 to I at -TH2 15 << x < -TH1, and 0 (x) linearly changes in the range of 1 to 0 at TH1 << x < TH2. However, when the condition "-TH2 < -THl < 0 < TH1 < TH2" is set, the function G3(x) is applied, [0107] 20 In this embodiment, although the configuration of the applied image processing apparatus is similar to that oi the second embodiment, corrected pixel values are calculated not by using the function (3(x) (refer to Expression 17) in the second embodiment but by using a function (3(x) having a 25 definition illustrated in Fig. 9(2) and using the previously described (Expression 15) and (Expression 16). As a result, the boundary between the flat portion and the edge portion is smoothed, and the generation of the artifact due to the switching can be prevented. 30 [0108] 4. Regarding an example of sensitivity difference 34 SP263074W000 correction processing in which an edge portion is considered (fourth embodiment) Next, an example of sensitivity difference correction processing in which an edge portion is considered like the S second embodiment and the third embodiment is described as a fourth embodiment of an image processing apparatus of the invention. [0109] The fourth embodiment is an embodiment obtained by 10 changing the function (3(x) like the third embodiment. In addition, in the present embodiment, (Expression 15) and (Expression 16), which have been applied as expressions for calculating correctedpixe].values inthe previously described second and third embodiment, are not used, but new expressions 15 (Expression 18) and (Expression 19) to be described below are used, [0110] When an interest pixel is Gb, a G pixel value G (-) , the sensitivity of which is corrected using the following 20 (Expression 18), is calculated. Moreover, when the interest pixel is Gr, the G pixel value G(-) , the sensitivity of which is corrected using the following (Expression 19), is calculated. [0111] 25 [Formula 15] G =Gb+y (mGr-rnGb 2 i ...(Expression 18) 35 SP263074WO00 G=Gr+y(rn&b - mGr ) 2 .,.(Expression 19) [0112] A function y(0) in the above-mentioned (Expression 18) 5 and (Expression 19) is a function defined by the following (Expression 20). [0113] [Formula 16] AX) _ x I X H< lH 0 otherwise 10 ...(Expression 20) [0114] In the above-mentioned (Expression 20) , TH is a threshold parameter to separate a flat portion and an edge portion from each other. As a function7(x) defined in the above-mentioned 15 (Expression 20), various functions maybe used. However, the function illustrated in Fig. 10(1) is used for example. That is, 7(x) = 0 at x < -TH or TH < x, and y (x) linearly changes in the range of -1 to 1 at -TH < x < TH. The function y(x) with such a setting is used. 20 [0115] In the present embodiment, although the configuration of the applied image processing apparatus is similar to the configuration applied in the second embodiment, corrected pixel values are calculated not by using (Expression 15) to 25 (Expression 17) used in the second embodiment but by applying the above-mentioned (Expression 20), that is, by applying the function y(x) having a definition illustrated in Fig. 10(1) 36 SP263074WO00 and by applying the previously described (Expression 18) and (Expression 19). [0116] 5. Regarding an example of sensitivity difference 5 correction processing in which an edge portion is considered (fifth embodiment) Next, an example of sensitivity difference correction processing in which an edge portion is considered like the second embodiment to the fourth embodiment is described as 10 a fifth embodiment of an image processing apparatus of the invention. [0177] The fifth embodiment is an embodiment obtained by changing the function y(x) in the fourth embodiment which has 15 been described with reference to (Expression 20) and Fig. 10(1). [0118] In the fifth embodiment, the function 7(x) is set as illustrated in Fig. 10(2). That is, 20 y(x) = 0 at x < -TH3 or TH3 < x, and 7(x) =1 at -TH2 < x < Till or Till < x < TH2. Moreover, 7(x) linearly changes in the range of 0 to -1 at -TH3 << x < -TH2, y(x) linearly changes in the range of -1 to 1 at -TI11 < x < THl, and y(x) linearly changes in the range of 1 to 0 25 at TH2 < x < TH3. However, the function y(x) with the setting of -TH3 < -TH2 < -TH7. < 0 < TH1 Ev" is established, that is, when there is a stronger edge in the horizontal direction and it is determined that a correlation with the vertical direction is strong, the pixel value of the 25 G pixel is calculated by using the following pixel value calculation expression (Expression 27). [0150] [Formula 22] 45 SP263074WO00 G1 G4 2 (Expression 27) [0151] As illustrated in Fig. 16(A), G1, G2, G3, and G4 are 5 G pixels adjacent to the interest pixel. The above-mentioned expression is an expression to calculate an estimated pixel value of the G pixel at the position of the R pixel or the B pixel by using the G pixel value of the horizontal direction. That is, demosaic processing of determining the pixel value 10 of the processing target, pixel is performed by setting contribution of the pixel value of the reference pixel in a direction where a change in the pixel value is small to a high level. [0152] 15 (2) G pixel value calculation processing for a position of a G pixel Next, Gpixelvalue calculationprocessingforaposiLion of a G pixel is described. When a center pixel (interest pixel) is a G pixel as; illustrated in Fig. 16(B), the following 20 (Expression 28) is applied and the pixel value of the G pixel is used as it is. [0153] [Formula 23] G=G5 25 eve(Expression 28) [0154] When the center pixel (interest pixel) is a G pixel as illustrated in Fig, 16(B), the pixel value is used as it is. 46 SP263074WO00 [0155] G pixels at all pixel positions are obtained based on the above-mentioned (Expression 26), (Expression 27), and (Expression 28) a As for the G pixel value used at the time 5 of performing the demosaic processing, it is desirable to use the G pixel values corrected according to each embodiment described above as pixel values of the Or pixel and the Gb pixel. [0156] 10 An R/B high frequency generating unit 152 calculates an R pixel and a B pixel for each position of all pixels by using the G pixel, a mean value mR of R adjacent to the interest pixel which is calculated based on (Expression 21) by the R mean calculating unit 144, and a mean value mB of B adjacent 15 to the interest pixel which is cal culated based on (Expression 22) by the B mean calculating unit 145. That is, the interpolation processing of the R pixels and the B pixels is executed. [0157] 20 [Formula 24] R=( R- G)±G ...(Expression 29) A ( ---- mG)±G -(Expression 30) 25 [0158] The mR, mG, and mB in the above (Expression 29) and (Expression 30) are weighted mean values of surrounding pixels of the interest pixel which are calculated according to the 47 SP263074W000 and the Gr pixel with a DSP, a memory to store pixel values of adjacent pixels, for example, the line memory 141; the Gr mean calculating unit 142; the Gb mean calculating unit 143; and the sensitivity difference correcting unit 146 maybe used. 5 That is, there may be a common memory and a common processing unit used for the sensitivity difference correction processing and the demosic processing. Therefore, components necessary for both the processing may be integrated as illustrated in Fig. 12. 10 [01.62] Therefore, by realizing a configuration in which the operations described in the above embodiments are executable, with use of hardware which executes existing demosicprocess ing, a conf iguration inwhich thesensitivi_ty dif ference correction 15 processing as well as the demosaic processing is executed is achieved. [0163] 7. Regarding an embodiment (seventh embodiment) in which sensitivity difference correction processing and demosaic 20 processing are combined Next, modified processing of the embodiment (the :,i.xth embodiment), in which the sensitivity difference correction processing and the demosaic processing are combined, is described as a seventh embodiment of an image processing 25 apparatus of the invention. [0164] The image processing apparatus of the seventh embodiment has the configuration of the image processing apparatus, for example, illustrated in Fig. 4 like the previously described 30 first to fifth embodiments. In an imaging apparatus 100 illustrated in Fig. 4, light incident through an optical lens 49 SP263074WO00 101 is incident on an imaging device 102 configured by a CCD, a CMOS image sensor, or the like, and image data is output. The output image data is input to a DSP block 103, and signal processing for an output signal is performed here. After that, output image 104 is output. [0165] A configuration example of the DSP block 103 in the present embodiment has the configuration which has been described with reference to Fig. 11 like the above-described 10 sixth embodiment. [0166] A sensitivity difference correction and demosaic processing unit 131 of the present embodiment is described with reference to Fig. 17. 15 [0167] A line memory 141 is used to acquire pixel values of vertically adjacent pixels of an interest pixel. A Or mean calculating unit 142 is a block to undergo a weighted mean of the pixel values of Cr adjacent to the interest pixel. When 20 the weighted mean of Gr is assumed to be mGr, the mGr is calculated based on the previously described (Expressi(n 7) A Gb mean value calculating unit 142 is a block to undergo aweightedmean of the pixel values of Gb adjacent to the interest pixel. When the weighted mean of Gb is assumed to be mob, 25 the mGb can be calculated based on the previously described (Expression 8). [0168] In an R mean calculating unit 144, a mean value mR of R adjacent to the interest pixel is calculated based on the 30 previously described (Expression2l) Ina B mean calculating unit 145, a mean value mB of B pixels adjacent to the interest 50 SP263074WO00 pixel is calculated based on the previously described (Expression 22). [0169] In a direction determination processing unit 146, edge 5 estimation values in a horizontal direction and a vertical direction are calculated according to the previously described (Expression 23) and (Expression 24). The direction determination processing unit 146 calculates a horizontal-direction edge estimation value Eh and a 10 vertical-direction edge estimation value Ev. [0170] In an edge adding unit 161, edge component information which does not depend on the direction is calculated according to the following (Expression 31). 15 Ehv = Eh + Ev Expression 31) [0171] Edge components that do not depend on the direction are obtained based on the above-mentioned (Expression 31). The 20 value (edge component information) Ehv calculated based on the above-mentioned (Expression 31) has the following characteristic. The Ehv increases in an edge portion, and decreases in a flat portion. That is, the value has such a characteristic. 25 [0172] In the configuration that calculates the G pixel values as the corrected pixel values of a Gr pixel and a Gb pixel, by applying a function (3 (x) that produces a value in the range of 1 to 0 according to whether it is the edge portion, which 30 is described in the previously described second to fourth embodiments, weighted mean values mGr and mGb of ad.jacent.Gr 51 SP2630'74W000 and Gb pixels of the interest pixel, which are obtained based on (Expression 7) and (Expression 8) , are used in the previously described (Expression 15) to (Expression 20). The processing described in the second to fourth embodiments is 5 a method which does not deteriorate the edge portion while removing the artifact that appears in the flat portion due to the difference in the sensitivity between the Gb pixel and the Gr pixel. [0173] 10 Although the function (3 (x) that produces a value in the range of 1 to 0 according to whether it is an edge portion or not in the second to fourth embodiments, most suitable processing according to the determination result can be realized by determining whether it is the edge portion or the 15 flat portion even by using the Ehvwhich is calculated according to the above-mentioned (Expressi_ on 31) instead of the function Vx), [0174] Specifically, for example, the following (Expression 20 32) can be used instead of the function (3(x) of (Expression 17) which is described in the second embodiment. [0175] [Formula 25] AX) 1 Ehv c TH 0 otherwise 25 ...(Expression 32) [0176] In the above-mentioned (Expression 32) , TH is a threshold parameter used to separate the flat portion and the edge portion from each other. When edge component information (Ehv) , which 52 SP263074WO00 does not depend on the direction and is calculated based on the above-mentioned (Expression 31), is less than the preset threshold TI-I, (3(x) = 1. On the other hand, when the edge component information (Ehv) is the preset threshold TM or more, 5 (x) = 0. [0177] Thus, the invention may provide a configuration that calculates corrected pixel values of G pixels by using the edge component information (Ehv) , which does not depend on 10 the direction and is calculated based on the above-mentioned (Expression 31), and by using (Expression 15) and (Expression 16) described in the second embodiment. Even for the function (3(x) applied in the third and fourth embodiments, the above--mentioned (Expression 32) which uses the edge element 15 information (Ehv) , which does not depend on the direction and is calculated based on the above-mentioned (Expression 31), can be used. [0178] According to the processing of the invention, it is 20 possible to remove the artifact which especially appears in the flat portion of an image by correcting the sensitivity difference that exists between the color filters having the same spectral characteristic. One example that shows the effect according to the invention is described with reference 25 to Fig. 18. In Fig. 18, (A) an image without having been subjected to G pixel correction processing according to the invention and (B) an image having been subjected to the G pixel correction processing according to the invention are illustrated in parallel. 30 [0179] Although it is difficult to confirm because the figure 53 SP263074W000 illustrates an image, which is originally a color image, in gray scale, the artifact in the check appears in the image (A) which has not been subjected to the G pixel correction processing and it is observed that the artifact is reduced 5 in the image (B) which has been subjected to the G pixel correction processing according to the invention, [0180] Thus, with use of the configuration of the invention, it becomes possible to correct the sensitivity difference 10 between the color filters having the same spectral characteristic with a very little amount of operations. Moreover, the pixel value correction processing of the invention has a configuration similar to the configuration of existing demosaic processing, the operation and memory are 15 shared when the pixel value correction processing of the inventioni_sintegrated with the existing demosaicprocessing, and hardware may be built with a smaller amount of operation and memory capacity, [0181] 20 8. Regarding a hardware configuration example of an image processing apparatus Lastly, a specific hardware configuration of one image processing apparatus of the invention is described with reference to Fig. 19. Fig. 19 illustrates an example of a 25 personal computer (PC) as an example of the image processing apparatus of the invention. However, as described above, the image processing apparatus of the invention may be realized by any of various apparatuses such as an imaging apparatus, a TV, and a player as well as the PC as long as the apparatus 30 receives amosaic image, which is imaged by applying a specific color filter to a single plate-type image sensor and can perform 54 P2630'74WO00 the demosaic processing. [0182] A Central Processing Unit (CPU) 501 executes various processing according to a program stored in a Read Only Memory 5 (ROM) 502 or a storage unit 508. For example, the CPU executes brightness control processing described in each of the embodiments described above. Programs executed by the CPU 501, data, etc. are properly stored in a Random Access Memory (RAM) 503. The CPU 501, the ROM 502, and the RAM 503 are 10 connected to one another by a bus 504. [0183] The CPU 501 is connected to an input/output interface 505 via the bus 5C4. The input/output interface 505 is connected to an input unit 506 configured by a keyboard, a 15 mouse, a microphone, etc; and an output unit 507 configured by a display, a speaker, etc. Moreover, processing target data, for example, the mosaic image (the photoelectric conversion signal) imaged by applying a specific color filter to a single plate-type image sensor is input through the input 20 unit 506. [0184] The CPU 501 executes various processing corresponding to instructions input from the input unit 506 and outputs processing results, for example, to the output unit 507. The 25 output unit 507 is configured by a display, a speaker, etc., and the image generated by the above-described processing is displayed on the display. [0185] The storage unit 508 connected to the input/output 30 interface 505 is configured, for example, by a hard disk, and stores programs to be executed by the CPU 501, and various 55 SP263074W000 kinds of data. The communication unit 509 communicates with an external device through a network such as the Internet and a local area network. [0186] 5 The drive 510 connected to the input/output interface 505 drives a removable medium 511 such as a magnetic disc, an optical disc, a magneto optical disc, and a semiconductor memory and acquires recorded programs, data, etc. The acquired program and data are transmitted to and stored in 10 the storage unit 508 as necessary. [0187] Hereinabove, the invention has been described in detail with reference to a specific example. However, it is apparent that those skilled in the art may make changes or substitutions 15 to the embodiments without departing from the spirit of the invention. That is, the invention has been disclosed in the form of illustrations, and the invention should not be interpreted limitedly. Reference should be made to the appended claims, in order to assess the scope of the invention. 20 [0188] Moreover, a series of processing which hasbeen desc^ _bed in the specification can be executed with a configuration of hardware, software, or a combination of both. When processing based on software is executed, the processing may be executed 25 by installing a program, which is a record of a process sequence, in a memory inside a computer which is built in dedicated hardware, or by installing a program in a general purpose computer in which various kinds of processing can be performed. For example, the program maybe recorded in a recording medium 30 beforehand. Besides the installation from a recording medium to a computer, the program may be received through a network 56 SP263074WO00 such as a Local Area Network (LAN) and is then installed in a recording medium such as a built-in hard disc, [0189] Various processing described in the specification may 5 not only be executed in time series manner according to the order of description, but also be executed in parallel or individually according to processing capacity of an apparatus which executes the processing or as necessary. The term "system" in this specification means a configuration of a 10 logical set of a plurality of devices, but the each device is not necessarily provided in the same casing, INDUSTRIAL APPLICA2ILITY [0190] 15 As described above, according to a configuration of one example of the invention, provided are a device and a method that execute sensitivity correction processing on an image signal generated by a single plate-type image sensor through a color filter. Specifically, the sensitivity difference 20 correction of Gr and Gb signals included in an image signal, for example, an RGB signal, generated by a single platetype image sensor through a color filter is executed, Apixelvalue of a color filter unit which has the same color as a correction target pixel and is provided in surroundings of the correction 25 target pixel is acquired, A difference between weighted mean pixel values "a" and "b" of two kinds of pixel groups "A" and "B" classified according to positions of pixels is added to a pixel value of the correction target pixel to calculate an additional value. A mean value of the pixel value of the 30 correction target pixel and the additional value is calculated as a corrected pixel value of the correction target pixel. 57 SP263074WO00 According to the processing of the present invention, correction processing can be performed with a simple operation and with high accuracy. 5 REFERENCE SIGNS LIST [0191] 100 Imaging apparatus (Image processing apparatus) 101 Optical lens 102 Imaging device 10 103 DSP block 104 Output image 111 Sensitivity difference correction processing unit 112 White balanca processing unit 113 Demosaic processing unit 15 114 Gamma correcting unit 115 YC converting unit 121 Gr mean value calculating unit 122 Gb mean value calculating unit 123 Sensitivity difference correcting unit 20 131 White balance processing unit 141 Line memory 142 Gr mean value calculating unit 143 Gb mean value calculating unit 144 R mean value calculating unit 25 145 B mean value calculating unit 146 Direction determination processing unit 147 Sensitivity difference correcting unit 148 G mean calculating unit 149 Correlation processing unit 30 151 G high frequency generating unit 152 R/B high frequency generating unit 58 SP263074W000 161 Edge adding unit 162 Sensitivity difference correcting unit 501 CPU 502 ROM 5 503 RAM 504 Bus 505 Input/output interface 506 Input unit 507 Output unit 10 508 Storage unit 509 Communication unit 510 Drive 511 Removable medium 59 SP263074WO00 CLAIMS 1. An image processing apparatus comprising: a sensitivity difference correction processing unit 5 that receives a photoelectric conversion signal and executes sensitivity difference correction processing, the photoelectric conversion signal being output by an image sensor based on incident light being incident through a color filter, wherein the sensitivity difference positive processing 10 unit: acquires a pixel value of a color filter unit which has a same color as a correction target pixel and is present in surroundings of the correction target pixel; calculates an additional value by adding a difference between weighted mean pixel values "a" and "b" of two ]rinds of pixel groups "A" and 15 "B" classified according to positions of the pixels to the pixel value of the correction target pixel, the weighted mean pixel values corresponding to distances of the pixel groups from the correction target pixel; and calculates a mean value of the pixel value of the correction target pixel and the 20 additional value as a corrected pixel value of the correction target pixel. 2. The image processing apparatus according to claim 1, wherein 25 the color filter is arrayed in a Bayer pattern, and the sensitivity difference correction processing unit has a configuration which a sensitivity difference between an Gr pixel and a Gb pixel included in an image which is imaged through the color filter of the Bayer pattern is corrected. 30 3. The image processing apparatus according to claim 2, 60 SP263074WO00 wherein the sensitivity difference correction processing unit: calculates, when performing correction processing on the Gr pixel and the Gb pixel, weighted pixel value means mGr and 5 mGb corresponding to distances of the Gr pixel and the Gb pixel, which are adjacent to the correction target pixel, from the correction target pixel; calculates an additional value by adding a difference between the mGr and the mGb to the pixel value of the correction target pixel; and calculates the mean 10 value of the pixel value of the correction target pixel and the additional value as the corrected pixel value of the correction target pixel, 4 e The image processing apparatus according to any one of 15 claims I to 3, wherein the sensitivity difference correction processing unit: calculates a final corrected pixel value by reducing a contribution level of the additional value when an adjacent image area including the correction target pixel is an edge 20 area; and calculates the final corrected pixel value by increasing the contribution level of the additional valuf- when the adjacent image area including the correction target pixel is a flat area. 25 5. The image processing apparatus according to any one of claims 1 to 4, wherein the sensitivity difference correction processing unit has a configuration in which demosaic processing is executed. 30 6. The image processing apparatus according to claim 5, wherein 61 SP263074W000 correction processing, wherein the sensitivity difference positive processing executes acquiring a pixel value of a color filter unit which has a same color as a correction target pixel and is present 5 in surroundings of the correction target pixel; calculating an additional value by adding a difference between weighted mean pixel values "a" and "b" of two kinds of pixel groups "A" and "B" classified according to positions of pixels, the weighted pixel.. value means corresponding to distances of the 10 pixel groups from the correction target pixel, to a pixel value of the correction target pixel; and calculating a mean value of the pixel value of the correction target pixel and the additional value as a corrected pixel. value of the correction target pixel. 15 10, A program that causes image processing to be executed in an image processing apparatus and causes a sensitivity difference correction processing unit to receive a photoelectric conversion signal that is output by an image 20 sensor based on incident light being incident through a color filter, and to execute sensitivity difference correction processing, wherein the sensitivity difference positive processing executes: acquiring a pixel value of a color filter unit which 25 has a same color as a correction target pixel and is present in surroundings of the correction target pixel; calculating an additional value by adding a difference between weighted mean pixel values "a" and "b'" of two ]rinds of pixel groups "A" and "B" classified according to positions of pixels, the 30 weighted pixel value means corresponding to distances of the pixel groups from the correction target pixel, to a pixel value 63 SP263074W000 of the correction target pixel; and calculating a mean value of the pixel value of the correction target pixel and the additional value as a corrected pixel value of the correction target pixel.