JP4225414B2 - Image color correction apparatus, method, program, and recording medium - Google Patents

Description

  An object illuminated by light having a spectrum different from that of sunlight, such as an incandescent bulb, exhibits an apparent color different from that of illumination under standard sunlight. In the present invention, for example, when an image taken under sunlight is subjected to color correction, converted into an image under an incandescent light bulb, and displayed on a CRT or the like, the color sense under the sunlight is the same. The present invention relates to a color appearance image technology for making images visible. Here, the color appearance image is an image for generating, under the second illumination light, the same sensation as the color sensation felt by the person observing the object under the first illumination light.

Nayatami Y., Takahama K., Sobagaki H. and Hashimoto K., “Color-appearance model and chromatic adaptation transform”, Color Research and Application, 15, 210-221 (1990) Hunt R.W.G., “Revised color-appearance model for related and unrelated colors”, Color Research and application, 16, 146-165 (1991) Kuriki I. and Uchikawa K., “Adaptive Shift of Visual Sensitivity Balance under Ambient Illuminant Change”, Journal of the Optical Society of America A, 15, 2263-2274 (1998)

  As a typical color correction formula used to match the apparent color when the lighting environment is different, the International Lighting Commission (CIE) has proposed CIE Color Appearance Model 97s (hereinafter referred to as CIECAM97s) as a standard formula. This is a synthesis of various color correction formulas proposed in the past. The data for deriving the color correction formula that is the basis of CIECAM97s uses color matching between the left and right visual fields using a device that adapts the left and right eyes to separate lighting spaces (binocular septum color matching method). It was acquired by the method to perform (refer nonpatent literature 1 and nonpatent literature 2). However, the situation where the left and right eyes adapt to different illumination light spaces is unusual, and rather the viewer spends more time in the space illuminated by one light. Sensitivity changes measured in extraordinary laboratory environments do not necessarily reflect the characteristics of human daily visual mechanisms, and visual sensitivity measurements are performed in a single illumination environment. Should.

  It is the periphery of the achromatic color that is most sensitive to color changes. Non-Patent Document 3 introduces objectively measuring the change in sensitivity by a method of adjusting the color of the presentation stimulus to an achromatic color. However, plotting the light chromaticity trajectory predicted by CIECAM97s to appear achromatic under certain lighting conditions draws a trajectory that differs from the psychophysically measured achromatic point.

  FIG. 5 shows a locus of colored light (achromatic point) that appears to be colored when it deviates even slightly from this point under each lightness / illumination light condition. Response ratio L / (L + M) of L cone (long wavelength cone) and M cone (medium wavelength cone) on the horizontal axis, and S cone (short wavelength cone) and L, M on the vertical axis It is a chromaticity diagram obtained by projecting a vector in a three-dimensional color space onto a luminance plane, a MacLeod-Boynton coordinate system having a cone response ratio S / (L + M). The three panels Sl, S2, S3 show the differences between subjects. The difference in symbol shape indicates the difference in chromaticity of the ambient illumination light. S1 and S2 were tested under 5 conditions, and S3 was tested under 3 conditions. The chromaticity of the illumination light is indicated by a gray symbol, and the achromatic point of the subject corresponding to each illumination condition is indicated by a white symbol having the same shape. A plurality of white symbols are present because achromatic color point adjustment is performed at five levels of luminance, and the luminance effect is shown in FIG.

  The measurement was repeated 25 times for each point condition, and the average value was shown. The error par indicating the standard deviation is shown only in Fig. 6 because of the legibility of the figure.The black symbols are the achromatic points predicted by CIECAM97s under the illumination conditions of the corresponding symbol shapes. A certain chromaticity is predicted regardless of (luminance).

  FIG. 5 shows that although the chromaticity (white symbol) of light perceived by humans as an achromatic color changes with the brightness of the observation object, CIECAM97s (black symbol) does not predict the change. I can read. FIG. 6 is a replot of the same data with the relative luminance of the observation target as the horizontal axis and the opposite color response φ (= L / M) on the vertical axis. While the chromaticity (white symbol) of light perceived as achromatic color changes according to lightness, the achromatic color point predicted by CIECAM97s (black symbol + broken line) predicts a constant value regardless of lightness 5 and 6, when the light that should be seen as an achromatic color deviates from the trajectory of the psychophysical experiment result shown in the white symbol, the phenomenon that the color appears to appear is generated. It will be incomplete as a prediction of appearance. In this regard, the prior art has a major error.

  As described above, in the past technology, the binocular septum color matching method, which is an extraordinary observation environment, was used as an equation to approximate the apparent color change that occurs when the illumination light changes. There is a problem that it is inappropriate for application to the environment. In addition, since it is not explicitly considered that the achromatic color point changes according to the brightness of the object, there is a problem that an object that should not be colored is colored.

  An object of the present invention is to solve the above problems and to perform color correction on an image under different illumination light displayed on a CRT or the like to convert it into a color appearance image close to vision.

  The present invention utilizes the fact that the tristimulus value vector (X, Y, Z), which is a photometric value of an image, and the cone response vector (L, M, S) representing visual sensitivity are in a linear relationship. Then, from the color information of two different illumination lights and the brightness of the standard white plate under one illumination light, color correction is performed on the image observed and photographed under the illumination light, so that the other illumination light It is characterized in that a color appearance image close to vision below is obtained.

  According to the present invention, a color appearance image under the other illumination light is obtained by performing color correction on an image observed under one illumination light using a parameter having a relationship between human visual sensitivity and linear transformation. Looking for. Therefore, an image under different illumination light can be displayed at high speed on a CRT or the like.

In particular, the problem of coloring an object that should not be colored when converting an image observed under non-standard white illumination light into an image under standard white light has been solved. An image close to can be obtained.

  A cone response vector is obtained from the color information of the illumination light observed and photographed and the illumination light to be converted. Then, the color information of each pixel of the image observed and photographed under the illumination light is converted into a cone response vector, and correction is performed using the cone response vector of each illumination light. Get a color appearance image under.

を用いて、測定対象の分光放射輝度I(λ)に対する三刺激値ベクトル(X, Y, Z)は(1)〜(3)式のように定義されている。

はJISなどの工業規格で定義されている最大視感度という定数である。この三刺激値ベクトル(X, Y, Z)は人間の視覚感度と線形変換の関係にある。 The tristimulus vector (X, Y, Z) is a measurement of light established by the International Lighting Commission CIE in 1931. Color matching function shown in FIG.

Is used to define the tristimulus value vector (X, Y, Z) with respect to the spectral radiance I (λ) of the measurement object as shown in equations (1) to (3).

Is a constant called the maximum visibility defined by industrial standards such as JIS. This tristimulus value vector (X, Y, Z) is related to human visual sensitivity and linear transformation.

を用いて、(4)〜(6)式のように定義されている。

三刺激値ベクトル(X, Y, Z)は、SmithとPokorny (1975)による次の(7)式により錐体応答ベクトル(L, M, S)に変換できる。

L、M、Sはそれぞれ長波長、中波長、短波長に最大感度を持つ視細胞の応答量を表している。この錐体応答ベクトルを用いて、画像色の補正を行なう。 The cone response vector (L, M, S) is the human cone spectral sensitivity shown in Fig. 8.

Is defined as in the equations (4) to (6).

The tristimulus value vector (X, Y, Z) can be converted into a cone response vector (L, M, S) by the following equation (7) by Smith and Pokorny (1975).

L, M, and S represent the amount of response of photoreceptor cells having maximum sensitivity at long wavelength, medium wavelength, and short wavelength, respectively. The cone color is used to correct the image color.

FIG. 1 is a block diagram of an image color correction apparatus according to an embodiment of the present invention. This uses a cone response vector to convert an input image 1 taken under non-standard white illumination light into an output image 22 (
Color appearance image).
Color information of the photographed input image 1 non-standard white illumination light, i.e., tristimulus values vector, to convert environmental illumination color information acquisition unit 7 cone response vector _{(C L, C M, C} S) to. At this time, Equation (7) is used. Further, the reference luminance S _B is obtained through the reference luminance acquisition unit 8 from the reflected light from the standard white plate under the non-standard white illumination light.

この輝度I_Bから、輝度コントラストI_Cを輝度コントラスト算出部１１において求める。

輝度コントラストI_Cは、輝度コントラスト比較部１７において色補正を行なうべきか否かを判断するときに利用される。輝度コントラストI_Cがモード係数k_modを超える場合は、色補正係数ベクトル(k_L, k_M, k_S)を (1.0, 1.0, 1.0)とする。モード係数k_modは、表面反射率100%の白色表面からの反射光強度を1.0としたときに反射物が発光体に見え始めるための最小輝度の比を表したもので、2.0〜3.0の値をとる。 Pixel color information at a certain point of the input image 1 taken under non-standard white illumination light, that is, a tristimulus value vector, is converted into a cone response vector (I _L , I _M , I _S ) by the pixel information input unit 6. Convert. At this time, equation (7) is used. The (8) by taking the sum of the response of having visual cell maximum sensitivity to the long wavelength and medium-wavelength as shown in the expression can be determined luminance I _B at the point described above.

From this luminance I _B , the luminance contrast I _{C is obtained} by the luminance contrast calculator 11.

The luminance contrast I _C is used when the luminance contrast comparison unit 17 determines whether or not to perform color correction. When the luminance contrast I _C exceeds the mode coefficient k _mod , the color correction coefficient vector (k _L , k _M , k _S ) is set to (1.0, 1.0, 1.0). The mode coefficient k _mod represents the ratio of the minimum luminance for the reflector to begin to appear as a light emitter when the reflected light intensity from a white surface with a surface reflectance of 100% is 1.0, and is a value between 2.0 and 3.0 Take.

次に係数a_φ、b_φ、a_ζ、b_ζを算出する。

ここでDは画像中の輝度ダイナミックレンジの対数値を表している。通常2.0〜3.0の値を用いる。これらの係数から、色補正係数ベクトル(k_L, k_M, k_S)を求めるのに必要な中間補正係数k_φ、k_ζを計算する。

When the value of the luminance contrast I _C is equal to or less than the mode coefficient k _mod , the nonlinear sensitivity change calculation unit 21 performs the following calculation to obtain the color correction coefficient vector (k _L , k _M , k _S ). First, the cone response vector (C _L , C _M , C _S ) of non-standard white illumination light and the cone response vector (S _L , S _M , S _S ) of standard white illumination light are respectively expressed in opposite color coordinates (φ _obj , Ζ _obj ), (φ _std , ζ _std ). That is,

Next, coefficients a _φ , b _φ , a _ζ and b _ζ are calculated.

Here, D represents the logarithmic value of the luminance dynamic range in the image. Usually, a value of 2.0 to 3.0 is used. From these coefficients, intermediate correction coefficients k _φ and k _ζ necessary for obtaining the color correction coefficient vector (k _L , k _M , k _S ) are calculated.

FIG. 4 is a conceptual diagram for calculating the intermediate correction coefficient (k _φ , k _ζ ). (k _φ , k _ζ ) takes a value between the opposite color coordinates (φ _obj , ζ _obj ) of the non-standard white illumination light and the opposite color coordinates (φ _std , ζ _std ) of the standard white illumination light, which is It is determined by the luminance contrast I _C. If k _mod = 2.0, it is determined linearly with respect to the logarithmic value of I _C when the luminance contrast I _C is between 0.2% and 200%.

The color correction coefficient vectors (k _L , k _M , k _S ) are obtained using the equations (20) to (22) using the above intermediate correction coefficient.

Correction is performed by multiplying each component of the color correction coefficient vector (k _L , k _M , k _S ) by each component of the cone response vector (I _L , I _M , I _S ) at a certain point in the input image 1. The later cone response vectors (O _L , O _M , O _S ) are obtained. That is,

The corrected cone response vector (O _L , O _M , O _S ) is multiplied by the inverse matrix of the cone transformation matrix shown in Eq. (7) to convert it to a stimulus value vector. The pixel of the output image 22 is obtained by converting into a suitable general-purpose image signal.
By repeating the above operation for all the pixels of the input image 1, an output image 22 converted into a color appearance under standard white illumination light is obtained.

FIG. 2 shows a method for converting an input image 1 photographed under non-standard white illumination light into an output image (color appearance image) under standard white illumination light based on the image color correction apparatus of FIG. .
Immediately after the start of conversion (step S101), the environmental illumination light color information acquisition unit 7 converts the color information of the non-standard white illumination light into a cone response vector (step S102). Further, the reference luminance acquisition unit 8 obtains the reference luminance from the reflected light 5 of the standard white plate under the nonstandard white illumination light (Step S103). Further, the standard white illumination light color information acquisition unit 24 converts the standard white illumination light into a cone response vector (step S104).
Thereafter, the first pixel of the input image 1 is selected (step S105), and the color information of the pixel selected by the pixel information input unit 6 is converted into a cone response vector (step S106). The luminance contrast calculation unit 11 obtains the luminance contrast of the selected pixel from the luminance of the selected pixel and the reference luminance obtained in step S103 (step S107).
The contrast comparison unit 17 compares the luminance contrast with the mode coefficient (step S108). When the luminance contrast is less than or equal to the mode coefficient, the nonlinear correction coefficient calculation unit 21 calculates three color correction coefficients (step S110). The calculation method is as described in FIG. Thereafter, the pixel information output unit 14 performs correction by multiplying each component of the cone response vector of the pixel obtained in step S106 by a color correction coefficient (step S111).

  When the luminance contrast is larger than the mode coefficient in step S108, or when step S111 is completed, the process proceeds to step S112. Here, when the luminance contrast is larger than the mode coefficient, the cone response vector of the pixel is converted into a general-purpose image signal adapted to the characteristics of the display medium.

  Thereafter, it is determined whether or not conversion has been completed for all pixels (step S113). If there is a pixel that has not been converted, the next pixel is selected (step S114), and the process proceeds to step S106 to repeat the same operation. When the conversion has been completed for all the pixels, the conversion is completed (step S115).

  A program for executing the image color correction method shown in FIG. 2 and a recording medium on which this program is recorded are included within the scope of the present invention.

  FIG. 3 is a block diagram of an image correction apparatus according to another embodiment of the present invention. This is to convert an input image 1 taken under standard white illumination light into an output image 22 (color appearance image) under non-standard white illumination light.

以下実施例１と同じ方法で汎用の画像信号に変換して、非標準白色照明光の下での出力画像２２（カラーアピアランス画像）を得る。 The method for obtaining the luminance contrast from the color signal of each pixel of the input image 1 is the same as in the first embodiment. The correction coefficient output unit 23 is constituted by a storage device, for example. In this storage device, color correction coefficient vectors (k _L , k _M , k _S ) for each luminance contrast value under the target non-standard white illumination light are recorded as a table. The pixel information output unit 14 uses the read color correction coefficient vectors (k _L , k _M , k _S ) and executes the following calculations (26) to (28) to generate non-standard white illumination light. Find the lower cone response vector.

Thereafter, it is converted into a general-purpose image signal in the same manner as in the first embodiment, and an output image 22 (color appearance image) under non-standard white illumination light is obtained.

  The correction coefficient output unit 23 is not limited to a storage device, and as shown in FIG. 1, the contrast comparison unit 11, the nonlinear correction coefficient calculation unit 21, the environmental illumination light color information acquisition unit 7, and the standard white illumination light color information acquisition unit 24. The color correction coefficient vector may be obtained from the cone response vectors of the non-standard white illumination light and the standard white illumination light.

  An input image taken under the first non-standard white illumination light is converted into an output image (color appearance image) that produces realistic vision under the second non-standard white illumination light. In this case, an apparatus similar to that shown in FIG. 1, the same apparatus as that shown in FIG. 3, or a combination of these may be used. In the case of using the same apparatus as in FIG. 1, it is necessary for the environmental illumination light color information acquisition unit 7 to obtain two cone response vectors in order to obtain the cone response vectors of the first and second non-standard white illumination lights. is there.

これらの式を利用して各画素の錐体応答ベクトルに補正を施した後、汎用の画像信号に変換することにより、第二の非標準白色照明光の下での出力画像（カラーアピアランス画像）を得る。 The color correction coefficient vector of the first non-standard white illumination light for a pixel on the input screen is (k _1L , k _1M , k _1S ), and the color correction coefficient vector of the second non-standard white illumination light is (k _2L , k _2M , k _2S ), the correction equations for the pixel cone response vectors are (29) to (31).

Using these equations, the cone response vector of each pixel is corrected and then converted into a general-purpose image signal. This results in an output image (color appearance image) under the second non-standard white illumination light. Get.

  Similar to the first embodiment, image color correction methods, programs, and recording media corresponding to the second and third embodiments are also included in the scope of the present invention.

1 is a block diagram of an image color correction apparatus according to Embodiment 1 of the present invention. It is a flowchart which shows operation | movement of the image color correction apparatus by Example 1 of this invention. It is a block diagram of the image color correction apparatus by Example 2 of this invention. It is a conceptual diagram which shows the method of calculating a color correction coefficient vector in the nonlinear correction coefficient calculation part 21 of FIG. A graph showing the difference between the chromaticity trajectory of light predicted by CIECAM97s to appear achromatic and the psychophysical measurement trajectory, and the horizontal axis is the ratio L / (L The vertical axis represents the response ratio S / (L + M) of the S cone, L, and M cone. This graph shows the difference between the chromaticity trajectory of light that CIECAM97s looks achromatic and the trajectory measured psychophysically. The horizontal axis is relative luminance, and the vertical axis is the opposite color response φ = L / M. I have to. It is a graph of the color matching function used when calculating | requiring a tristimulus value vector. It is a graph which shows a human cone spectral sensitivity.

Claims (8)

An image color correction device for obtaining an output image under a second illumination light from an input image taken under a first illumination light,
The tristimulus vector, which is the color information of the first illumination light, is used as the response amount C of the L cone. _L And C cone response C _M And C cone response C _S Cone response vector of the first illumination light (C _L , C _M , C _S Environmental light color information acquisition unit that converts to
Reference brightness S from reflected light from a standard white plate under the first illumination light _B A reference luminance acquisition unit for calculating
The tristimulus value vector which is the color information of the pixel at a certain point of the input image is represented by the response amount I of the L cone. _L And M cone response I _M And S cone response I _S Pixel cone response vector (I _L , I _M , I _S ) And said I _L And I _M And luminance I _B A pixel information input unit for calculating
I _B The reference brightness S _B Divide by brightness contrast I _C A luminance contrast calculation unit for calculating
The brightness contrast I _C And a mode coefficient representing the ratio of the minimum luminance for the reflector to begin to appear as a light emitter when the reflected light intensity from a white surface having a surface reflectance of 100% is 1.0, and the luminance contrast I _C Is greater than the mode coefficient, the color correction coefficient k for the response amount of the L cone _L Correction coefficient k for response of M and M cones _M Correction coefficient k for S and S cones _S And a luminance contrast comparison unit each of which is 1.0,
The brightness contrast I _C Is less than the mode coefficient, the C _L The C _M Divided by _obj To calculate C _L The C _M And C _S Ζ _obj The opposite color coordinate of the first illumination light (φ _obj , ζ _obj ) And the response amount S of the L cone of the second illumination light _L The response amount S of the M cone in the second illumination light S _M Divided by _std The response amount S of the L cone of the second illumination light is calculated _L And the response amount S of the M cone of the second illumination light _M S cone response amount S in the second illumination light _S Ζ _std To calculate the opposite color coordinate of the second illumination light (φ _std , ζ _std ) Between the opposite color coordinates of the first illumination light and the opposite color coordinates of the second illumination light. _C Intermediate correction factor (k _φ , k _ζ ) And a color correction coefficient vector (k) corresponding to the response amount of each cone from the intermediate correction coefficient and the cone response vector of the first illumination light. _I , k _M , k _S ) For calculating the non-linear sensitivity change,
By multiplying each element of the color correction coefficient vector for the response amount of each cone with each element of the cone response vector of the pixel at a certain point under the first illumination light, respectively. The corrected cone response vector (O _L , O _M , O _S An image information output unit that obtains pixels of the output image under the second illumination light by converting each corrected cone response vector into a general-purpose image signal;
An image color correction apparatus comprising: An image color correction device that obtains an output image under non-standard white illumination light from an input image taken under standard white illumination light,
Reference brightness S from the reflected light from the standard white plate under the standard white illumination light _B A reference luminance acquisition unit for calculating
The tristimulus value vector which is the color information of the pixel at a certain point of the input image is represented by the response amount I of the L cone. _L And M cone response I _M And S cone response I _S The cone response vector of standard white illumination light (I _L , I _M , I _S ) And said I _L And I _M And luminance I _B A pixel information input unit for calculating
Luminance I _B The reference brightness S _B Divide by brightness contrast I _C A luminance contrast calculation unit for calculating
Correction factor k for response of L cone _L Correction factor for response of M and M cones _M Correction factor for response of S and S cones _S A color correction coefficient vector (k) for each luminance contrast value under the non-standard white illumination light composed of _L , k _M , k _S ), And a correction coefficient output unit that reads a color correction coefficient vector corresponding to the luminance contrast from the storage unit;
The reciprocal of each element of the read color correction coefficient vector and the pixel cone response vector (I _L , I _M , I _S ) By multiplying each element of the cone response vector under non-standard white illumination light (O _L , O _M , O _S ) And the cone response vector (O _L , O _M , O _S ) To a general-purpose image signal to obtain a pixel of an output image under the non-standard white illumination light, and a pixel information output unit,
An image color correction apparatus comprising: An image color correction device for obtaining an output image under a second illumination light from an input image taken under a first illumination light,
The ambient illumination light color information acquisition unit for calculating the cone response vector and the color correction coefficient vector of the first illumination light, and the cone response vector and the color correction coefficient vector of the second illumination;
A tristimulus value vector that is color information of a pixel at a certain point of the input image is converted into a cone response vector, and each element of the color correction coefficient vector of the first illumination light is converted to each element of the cone response vector. Is multiplied by each element of the color correction coefficient vector of the second illumination light to calculate a corrected cone response vector for each pixel, and the second illumination light is converted into a general-purpose image signal. A pixel information output unit for obtaining pixels of the output image under
The image color correction apparatus according to claim 1, further comprising: An image color correction device for obtaining an output image under a second illumination light from an input image taken under a first illumination light,
The tristimulus vector, which is the color information of the first illumination light, is used as the response amount C of the L cone. _L And C cone response C _M And C cone response C _S Cone response vector of the first illumination light (C _L , C _M , C _S A cone response vector conversion step of the first illumination light to be converted into
Reference brightness S from reflected light from a standard white plate under the first illumination light _B A reference luminance calculating step for calculating
The tristimulus value vector which is the color information of the pixel at a certain point of the input image is represented by the response amount I of the L cone. _L And M cone response I _M And S cone response I _S Pixel cone response vector (I _L , I _M , I _S ) And said I _L And I _M And luminance I _B A pixel information calculation step for calculating
I _B The reference brightness S _B Divide by brightness contrast I _C A luminance contrast calculating step for calculating
The brightness contrast I _C And a mode coefficient representing the ratio of the minimum luminance for the reflector to begin to appear as a light emitter when the reflected light intensity from a white surface having a surface reflectance of 100% is 1.0, and the luminance contrast I _C Is greater than the mode coefficient, the color correction coefficient k for the response amount of the L cone _L Correction coefficient k for response of M and M cones _M Correction coefficient k for S and S cones _S And luminance contrast comparison step, each of which is 1.0,
The brightness contrast I _C Is less than the mode coefficient, the C _L The C _M Divided by _obj To calculate C _L The C _M And C _S Ζ _obj The opposite color coordinate of the first illumination light (φ _obj , ζ _obj ) And the response amount S of the L cone of the second illumination light _L The response amount S of the M cone in the second illumination light S _M Divided by _std The response amount S of the L cone of the second illumination light is calculated _L And the response amount S of the M cone of the second illumination light _M S cone response amount S in the second illumination light _S Ζ _std To calculate the opposite color coordinate of the second illumination light (φ _std , ζ _std ) Between the opposite color coordinates of the first illumination light and the opposite color coordinates of the second illumination light. _C Intermediate correction factor (k _φ , k _ζ ) And a color correction coefficient vector (k) corresponding to the response amount of each cone from the intermediate correction coefficient and the cone response vector of the first illumination light. _I , k _M , k _S And a nonlinear sensitivity change calculation step for calculating
By multiplying each element of the color correction coefficient vector for the response amount of each cone with each element of the cone response vector of the pixel at a certain point under the first illumination light, respectively. The corrected cone response vector (O _L , O _M , O _S And a pixel of the output image under the second illumination light is obtained by converting each corrected cone response vector into a general-purpose image signal. An image color correction method for obtaining an output image under non-standard white illumination light from an input image taken under standard white illumination light,
Reference brightness S from the reflected light from the standard white plate under the standard white illumination light _B A reference luminance calculating step for calculating
The tristimulus value vector which is the color information of the pixel at a certain point of the input image is represented by the response amount I of the L cone. _L And M cone response I _M And S cone response I _S The cone response vector of standard white illumination light (I _L , I _M , I _S ) And said I _L And I _M And luminance I _B A pixel information calculation step for calculating
Luminance I _B The reference brightness S _B Divide by brightness contrast I _C A luminance contrast calculating step for calculating
Correction factor k for response of L cone _L Correction factor for response of M and M cones _M Correction factor for response of S and S cones _S A color correction coefficient vector (k) for each luminance contrast value under the non-standard white illumination light composed of _L , k _M , k _S ), And a correction coefficient output unit that reads a color correction coefficient vector corresponding to the luminance contrast from the storage unit;
The reciprocal of each element of the read color correction coefficient vector and the pixel cone response vector (I _L , I _M , I _S ) By multiplying each element of the cone response vector under non-standard white illumination light (O _L , O _M , O _S ) And the cone response vector (O _L , O _M , O _S Is converted into a general-purpose image signal to obtain pixels of an output image under the non-standard white illumination light. An image color correction method for obtaining an output image under a second illumination light from an input image photographed under a first illumination light,
The ambient illumination light color information calculating step for calculating the cone response vector and the color correction coefficient vector of the first illumination light, and the cone response vector and the color correction coefficient vector of the second illumination;
A tristimulus value vector, which is pixel color information at a certain point of the input image, is converted into a cone response vector, and each element of the color correction coefficient vector of the first illumination light is converted to each element of the cone response vector. Is multiplied by each element of the color correction coefficient vector of the second illumination light to calculate a corrected cone response vector for each pixel, and the second illumination light is converted into a general-purpose image signal. 5. The method of correcting an image color according to claim 4, wherein a pixel of an output image under is obtained. The program for making a computer perform the image color correction apparatus of any one of Claims 1 thru | or 3 . A computer-readable recording medium on which the program according to claim 7 is recorded.

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