Source: https://patents.justia.com/patent/6229916
Timestamp: 2019-05-27 12:08:42
Document Index: 184397190

Matched Legal Cases: ['art 1', 'art 1', 'art 1', 'art 1', 'art 1', 'art 2', 'art 1', 'art 2', 'art 2', 'art 2', 'art 2']

US Patent for Color transformation look-up table Patent (Patent # 6,229,916 issued May 8, 2001) - Justia Patents Search
Justia Patents Color CorrectionUS Patent for Color transformation look-up table Patent (Patent # 6,229,916)
Sep 30, 1998 - Fuji Photo Film Co., Ltd.
For example, as for how an image is to be transformed by considering the viewing conditions (such as the correlated color temperature of the white color, the luminance, and the ambient conditions) such that the same color appearances may be obtained when the image is viewed under certain conditions and when the image is viewed under different conditions, it has been proposed to employ transformation techniques which are ordinarily referred to as the chromatic adaptation transformation or chromatic adaptation models (i.e., color appearance models). The transformation techniques are described in, for example, Japanese Patent Publication Nos. 7(1995)-86814 and 7(1995)-86815; “Color Research and Application,” Volume 19, Number 1, 1994, R. W. G. Hunt; “Color Research and Application,” Vol. 20, No. 3, 1995, N. Nayatani; and “Color Research and Application,” Vol. 16, No. 4, 1991, M. D. Fairchild. As an appearance model, a Von Kries&apos;s chromatic adaptation prediction formula (a Von Kries&apos;s rule) is known as a basic one among various chromatic adaptation prediction formulas (“Color Engineering” by Noboru Ota, publishing office of Tokyo Denki University).
ii) a color transforming function for transforming the image signals for the non-self-luminous displaying medium into the image signals for the self-luminous displaying medium in accordance with a chromatic adaptation model (e.g., a chromatic adaptation model according to the Von Kries&apos;s chromatic adaptation rule) such that the appearances of perceived colors may become identical between the image displayed on the self-luminous displaying medium and the image displayed on the non-self-luminous displaying medium.
The major part 1 of the color direct transformation table forming apparatus (shown at a middle stage in FIG. 1) includes a parameter setting device 30, which receives information representing characteristic values of the non-self-luminous displaying medium, and the like, carries out a Von Kries&apos;s matrix calculation described later, and thereby sets parameters representing the degree of chromatic adaptation of the chromatic adaptation model of the non-self-luminous displaying medium. The major part 1 also device a lattice point signal setting device 40, which sets the signals of the RGB colorimetric system as lattice point signals Ei in the manner described later and in accordance with a color chart subjected to colorimetry. The major part 1 further comprises a dynamic range compensating means 50 for carrying out dynamic range compensation for transforming the dynamic range of color signals, which are capable of being reproduced on the non-self-luminous displaying medium, into the dynamic range of color signals, which are capable of being reproduced on the self-luminous displaying medium, in accordance with the non-self-luminous direct transformation relationship and the self-luminous inverse transformation relationship, the transformation being carried out for the respective lattice point signals Ei, which have been set by the lattice point signal setting device 40. The major part 1 still further includes a color transforming device 60 for carrying out color transformation for transforming the image signals for the non-self-luminous displaying medium into the image signals for the self-luminous displaying medium in accordance with the chromatic adaptation model such that the appearances of perceived colors may become identical between the image displayed on the self-luminous displaying medium and the image displayed on the non-self-luminous displaying medium, the transformation being carried out in accordance with the parameters, which have been set by the parameter setting device 30, and for the respective lattice point signals Ei, which have been set. The major part 1 also comprises a storage device 70 for storing the respective lattice point signals Ei, which have been set, and the corresponding image signals, which have been obtained from the dynamic range compensation and the color transformation.
The major part 2 of the color inverse transformation table forming apparatus (shown at a lower stage in FIG. 1) includes a parameter setting device 32. The parameter setting device 32 receives information representing the parameters, which have been set in the major part 1 of the color direct transformation table forming apparatus and represent the degree of chromatic adaptation of the chromatic adaptation model of the non-self-luminous displaying medium. The parameter setting device 32 also carries out a calculation of inverse parameters of the aforesaid parameters (in this case, a calculation of a Von Kries&apos;s inverse matrix). The major part 2 also includes a lattice point signal setting device 42, which sets the signals of the RGB calorimetric system as lattice point signals Fi in the manner described later and in accordance with a color chart subjected to colorimetry. The major part 2 further includes a dynamic range inverse compensation device 54 for carrying out dynamic range inverse compensation for transforming the dynamic range of color signals, which are capable of being reproduced on the self-luminous displaying medium, into the dynamic range of color signals, which are capable of being reproduced on the non-self-luminous displaying medium, in accordance with the self-luminous direct transformation relationship and the non-self-luminous inverse transformation relationship, the transformation being carried out for the respective lattice point signals Fi, which have been set by the lattice point signal setting device 42. The major part 2 still further comprises a color inverse transformation device 80 for carrying out color inverse transformation for transforming the image signals for the self-luminous displaying medium into the image signals for the non-self-luminous displaying medium in accordance with the chromatic adaptation model such that the appearances of perceived colors may become identical between the image displayed on the self-luminous displaying medium and the image displayed on the non-self-luminous displaying medium, the transformation being carried out in accordance with the inverse parameters, which have been set by the parameter setting device 32, and for the respective lattice point signals Fi, which have been set. The major part 2 also comprises a storage device 72 for storing the respective lattice point signals Fi, which have been set, and the corresponding image signals, which have been obtained from the dynamic range inverse compensation and the color inverse transformation.
Adaptive white: x&equals;0.3127, y&equals;0.3290 (D65)
Luminance: 160 cd/m2 to 640 cd/m2
Adaptive white: x&equals;0.3457, y&equals;0.3585 (D50)
Firstly, how the non-self-luminous direct transformation LUT forming device 12 and the non-self-luminous inverse transformation LUT forming device 14 operate will be described hereinbelow. (The combination of the two device 12 and 14 will hereinbelow be referred to as the non-self-luminous transformation LUT forming device 10.) As illustrated in FIG. 2 in detail, the non-self-luminous transformation LUT forming device 10 comprises an inverse transformation operation device 16 which utilizes the N-R technique, a Gamut outside signal estimating device 18, a direct transformation LUT forming device 19, and storage device 74, 75. With respect to the image signals for the DP, the non-self-luminous transformation LUT forming device 10 calculates the direct transformation relationship for the transformation from the RGB signal to the XYZ signals and the inverse transformation relationship for the transformation from the XYZ signals to the RGB signals. Pieces of information representing the calculated transformation relationships are stored as the LUT&apos;s in the storage device 74 and 75.
Firstly, the XYZ signals are calculated from the spectral distribution of the color patch and the spectral distribution of the illuminant, which have been obtained in the manner described above. The XYZ signals can be derived from Formulas (1), (2), and (3) shown below. x = K &it; &Integral; 380 780 &it; s &af; ( λ ) &it; ρ &af; ( λ ) &it; x &af; ( λ ) &it; &dd; λ ( 1 ) Y = K &it; &Integral; 380 780 &it; s &af; ( λ ) &it; ρ &af; ( λ ) &it; y &af; ( λ ) &it; &dd; λ ( 2 ) Z = K &it; &Integral; 380 780 &it; s &af; ( λ ) &it; ρ &af; ( λ ) &it; z &af; ( λ ) &it; &dd; λ ( 3 )
wherein S(&lgr;) represents the spectral distribution of the illuminant (&lgr; is the wavelength of light), &rgr;(&lgr;) represents the spectral reflectance distribution of the object, each of x(&lgr;), y(&lgr;), and z(&lgr;) represents the color matching function with respect to the human eyes, and the wavelength range of the visible light is set to be 380 nm to 780 nm. The normalization coefficient K is represented by Formula (4) shown below. K = 100 / &Integral; 380 780 &it; s &af; ( λ ) &it; y &af; ( λ ) &it; &dd; λ ( 4 )
As illustrated in FIG. 7, when the minimum density and the maximum density of the color patches of each of the R, G, and B colors are normalized to be 0 and 255, respectively, and the range of 0 to 255 is divided into eight stages, 512 (&equals;8×8×8) color patches are obtained. Also, values of the portions other than the measuring points at the lattice points in the color patches shown in FIG. 7 may be calculated with interpolating operations. In this manner, a non-self-luminous direct transformation table LUT1, which represents the relationship of the XYZ signals corresponding to the RGB signals of each color patch, can be obtained.
Firstly, target values on the lattice of the XYZ space are set to be (X0, Y0, Z0), and an allowable error in the repeated operations is set to be &Dgr;Emin. Thereafter, already known initial values (R1, G1, B1) in the RGB space are set, and stimulus values (X1, Y1, Z1) corresponding to the initial values (R1, G1, B1) are calculated. Also, the error quantity &Dgr;E between the target values (X0, Y0, Z0) and the stimulus values (X1, Y1, Z1) is calculated and compared with &Dgr;Emin. By way of example, the allowable error &Dgr;Emin may be set as a color difference, which is calculated in accordance with the color difference formula in the L*a*b* colorimetric system. In cases where the condition of &verbar;&Dgr;E&verbar;<&Dgr;Emin is not satisfied, correction values (&Dgr;R, &Dgr;G, &Dgr;B) are calculated, the initial values (R1, G1, B1) are corrected by the correction values (&Dgr;R, &Dgr;G, &Dgr;B), and the aforesaid processing is then repeated.
The afore said correction values (&Dgr;R, &Dgr;G, &Dgr;B) are calculated in the manner described below. Specifically, as illustrated in FIG. 9, when arbitrary RGB signals are given, the XYZ signals corresponding to the given RGB signals (represented by a point “a”) can be calculated by using XYZ signals (x0, y0, z0)&ap;(x7, y7, z7) corresponding to RGB signals (r0, g0, b0)&ap;(r7, g7, b7) at eight lattice points c0&ap;c7, the volume V of the rectangular parallelepiped surrounded by the lattice points c0&ap;c7, and volumes V0&ap;V7, which result from division of the rectangular parallelepiped by an arbitrary interpolation point “c” into eight sections. The calculations are made with Formulas (5), (6), and (7) shown below. X = &Sum; j = 0 7 &it; Vj &CenterDot; Xj / V ( 5 ) Y = &Sum; j = 0 7 &it; Vj &CenterDot; Yj / V ( 6 ) Z = &Sum; j = 0 7 &it; Vj &CenterDot; Zj / V ( 7 )
In the relationships of Formulas (5), (6), and (7), if it is assumed that the XYZ signals corresponding to the RGB signals are sectorial within a minute range, the correction values (&Dgr;R, &Dgr;G, &Dgr;B), which are minute change quantities of the RGB signals, and minute change quantities (&Dgr;X, &Dgr;Y, &Dgr;Z) of the XYZ signals will satisfy the relationship of Formula (8) shown below in accordance with the N-R technique. [ Δ &it; &it; X Δ &it; &it; Y Δ &it; &it; Z ] = [ &PartialD; X &PartialD; R &PartialD; X &PartialD; G &PartialD; X &PartialD; B &PartialD; Y &PartialD; R &PartialD; Y &PartialD; G &PartialD; Y &PartialD; B &PartialD; Z &PartialD; R &PartialD; Z &PartialD; G &PartialD; Z &PartialD; B ] &it; [ Δ &it; &it; R Δ &it; &it; G Δ &it; &it; B ] = J &af; [ Δ &it; &it; R Δ &it; &it; G Δ &it; &it; B ] ( 8 )
In Formula (8), J represents the Jacobian matrix. In Formula (8), when the Jacobian matrix J is determined, the minute change quantities (&Dgr;X, &Dgr;Y, &Dgr;Z) of the XYZ signals with respect to the correction values (&Dgr;R, &Dgr;G, &Dgr;B) of the RGB signals can be predicted. The Jacobian matrix J can be obtained by partially differentiating Formulas (5), (6), and (7) with the RGB signals. Therefore, the correction values (&Dgr;R, &Dgr;G, &Dgr;B) of the RGB signals can be calculated with Formula (9) shown below. [ Δ &it; &it; R Δ &it; &it; G Δ &it; &it; B ] = J - 1 &af; [ Δ &it; &it; X Δ &it; &it; Y Δ &it; &it; Z ] ( 9 )
Repeated operations may be carried out by using the Jacobian matrix J, which is obtained in the manner described above, and the RGB signals with respect to the arbitrary target values (X0, Y0, Z0) can there by be calculated. The same processing is carried out for all target values on the lattice in the XYZ space, and a first inverse transformation LUT for the transformation of the XYZ signals into the RGB signals is thereby formed.
With the N-R technique, it often occurs that the signals fall outside the color reproduction range during the convergent operation. Therefore, it is necessary that the RGB signals are virtually located at sufficiently remote positions outside the color reproduction range. In such cases, in an X-RG space illustrated in FIG. 10, points b1* and b2* may be set on the side outward from the color reproduction range. In such cases, if the points b1* and b2* do not retain the monotone relationship of smooth connection with respect to the relationship of points a1&ap;a4 within the color reproduction range, the operation will not converge. Therefore, such cases cannot be applied to the processing with the N-R technique.
Accordingly, after the N-R technique has been carried out by using the signals at the points b1* and b2*, such that the points b1*, b2* and the points a1&ap;a4 may have a monotone relationship, for example, virtual RGB signals RGB* and virtual XYZ signals XYZ* at the point b1* are calculated with the method of least squares by using only the signals at the points a1 and a2, which are close to the point b1*, and virtual RGB signals RGB* and virtual XYZ signals XYZ* at the point b2* are calculated by using only the signals at the points a3 and a4, which are close to the point b2*. Also, the relationship between the RGB signals, including the virtual RGB signals RGB*, and the XYZ signals, including the virtual XYZ signals XYZ*, is set as a second inverse transformation LUT.
T&equals;A.D (10)
Formula (10) represents the relationship of Formula (11) shown below. [ X Y Z ] = [ A X1 A X2 A X3 A X4 A Y1 A Y2 A Y3 A Y4 A Z1 A Z2 A Z3 A Z4 ] &it; [ R G B 1 ] ( 11 )
Further, the coefficient A, which satisfies the relationship of Formula (10), is calculated with the method of least squares such that E represented by Formula (12) may become minimum. In Formula (12), “i” represents the number of the color patch, and T represents the transposition of the rows and the columns of the matrix. E = &Sum; j &it; ( T i - A &CenterDot; D i ) &CenterDot; ( T i - A &CenterDot; D i ) T ( 12 )
When the coefficient A is calculated with Formula (12) shown above, the four-dimensional planes RGB-X, RGB-Y, and RGB-Z are determined. Thereafter, on the thus obtained four-dimensional planes RGB-X, RGB-Y, and RGB-Z, the virtual XYZ signals XYZ1*, which are located at a position sufficiently spaced from the XYZ signals, and the virtual RGB signals RGB1* corresponding to the virtual XYZ signals XYZ1* are calculated.
FIG. 11 shows the relationship between the XYZ signals, the virtual XYZ signals XYZ1*, and the RGB signals, the virtual RGB signals RGB1* which have been formed in the manner described above, as a two-dimensional profile diagram. Specifically, from the aforesaid findings, the relationship between the XYZ signals and the RGB signals is the monotone decreasing relationship as indicated by, for example, the points a1&ap;a4. Also, when the four-dimensional plane, which has been calculated with the method of least squares by using the points a1&ap;a4, is represented by the broken line, the plane connecting points b1, b2, which represent the virtual RGB signals RGB1* corresponding to the virtual XYZ signals XYZ1* on the four-dimensional plane, and the points a1&ap;a4 has a monotone decreasing relationship as indicated by the solid line. Therefore, in cases where the virtual RGB signals RGB1* with respect to the virtual XYZ signals XYZ1* are formed by using the method of least squares in the manner described above, the monotone relationship can be kept between the RGB signals containing the virtual XYZ signals XYZ1* and the XYZ signals containing the virtual RGB signals RGB1*.
How the self-luminous direct transformation LUT forming device 22 and the self-luminous inverse transformation LUT forming device 24 operate will be described hereinbelow. (The combination of the two device 22 and 24 will hereinbelow be referred to as the self-luminous transformation LUT forming device 20.) As illustrated in detail in FIG. 3, the self-luminous transformation LUT forming device 20 includes a calculation device 26, which makes calculations for the transformation of the RGB signals into the XYZ signals and thereby calculates the direct transformation relationship for the transformation from the RGB signals into the XYZ signals. The self-luminous transformation LUT forming device 20 also includes a calculation device 28, which makes calculations for the transformation of the XYZ signals into the RGB signals and thereby calculates the inverse transformation relationship for the transformation from the XYZ signals into the RGB signals. The self-luminous transformation LUT forming device 20 further includes a calculation device 29, which makes calculations for the transformation of the L*a*b* signals into the XYZ signals and thereby calculates the transformation relationship for the transformation from the L*a*b* signals into the XYZ signals. Pieces of information representing the calculated transformation relationships are stored as the LUT&apos;s in storage device 76 and 77. (Reference should be made to the upper left stage in FIG. 5.)
In the self-luminous transformation LUT forming device 20, basically, a table may be formed, which represents what colorimetric values of the XYZ calorimetric system are obtained when the respective RGB values are given as the image signals. Also, a table may be formed, which represents what signal values of the RGB calorimetric system are obtained when the signals of the XYZ calorimetric system are given. As for the NIFCRT, the signal correspondence relationship is defined by predetermined formulas in accordance with the chromaticity of the three primary colors, the chromaticity of the white point, and the &ggr; formula. Therefore, the correspondence relationship of signals can be obtained only from calculations without the NIFCRT image being measured. In this case, instead of the tables being formed, the mathematical formulas representing the correspondence relationship may be utilized directly.
In the cases of the NIFCRT, the LUT&apos;s should be set such that the signals falling outside the color reproduction range can be transformed. The calculations for such purposes may be made with the formulas shown below. R ′ &it; NIF = &it; R &af; ( 8 &it; &it; bits ) / 255.0 RNIF = &it; { ( R ′ &it; NIF + 0.055 ) / 1.055 } 2.4 &it; ( 0.03929 ≤q; R ′ &it; NIF ) RNIF = &it; R ′ &it; NIF / 12.92 &it; ( - 0.03929 < R ′ &it; NIF < 0.03929 ) RNIF = &it; - { ( - R ′ &it; NIF + 0.055 ) / 1.055 } 2.4 &it; ( R ′ &it; NIF ≤q; 0.03929 )
As for GNIF and BNIF, calculations may be made in the same manner as that shown above.
In the manner described above, with respect to the DP image signals and the NIFCRT image signals, respectively, the direct transformation tables LUT1, LUT3 for the transformation from the RGB signals into the XYZ signals and the inverse transformation tables LUT2, LUT4 for the transformation from the XYZ signals (the L*a*b* signals) into the RGB signals are obtained. Examples of the obtained LUT&apos;s are shown in FIGS. 4A, 4B, 4C, and 4D. With the thus obtained LUT&apos;s, the RGB signals for the DP can be transformed into the RGB signals for the NIFCRT such that the colorimetric values may coincide with each other between the DP image and the NIFCRT image.
For example, when desired values (Ri, Gi, Bi) are given as the RGB signals for the DP, the values (Xi, Yi, Zi) are calculated by using the non-self-luminous direct transformation table LUT1. Thereafter, when the values (Xi, Yi, Zi) are given, the RGB signals for the NIFCRT are calculated as (RO, GO, BO) by using the self-luminous inverse transformation table LUT4. FIG. 4E is an explanatory graph simply showing an example of the process for transforming the RGB signals for the DP into the RGB signals for the NIFCRT by using the LUT&apos;s shown in FIGS. 4A through 4 D. The right half of the graph of FIG. 4E shows the R and X signals in the LUT, which represents the correspondence relationship between the RGB signals and the XYZ signals for the NIFCRT. The left half of the graph of FIG. 4E shows the R and X signals in the LUT, which represents the correspondence relationship between the RGB signals and the XYZ signals for the DP. By way of example, in cases where the R value for the DP is 100, the X value for the DP may be 40.2. In such cases, a point P1 corresponding to such values is plotted on the line in the left half of the graph. Thereafter, a line is drawn horizontally from the plotted point P1 to the right half of the graph, and a point P2, at which the horizontally drawn line intersects with the line in the right half of the graph, is plotted. Also, a line is drawn between the point P2, and the R value for the NIFCRT, which corresponds to the X value of 40.2 for the NIFCRT, is thereby found as being approximately 90. With such a graph, the process for the signal transformation using the aforesaid LUT&apos;s would be understood easily. In this case, the interpolating operation is carried out by making reference to FIG. 4E. Actually, as described above, three-dimensional interpolating operations are carried out between lattice points.
In this embodiment, the Von Kries&apos;s chromatic adaptation model is considered. When the Von Kries&apos;s chromatic adaptation model is considered, it is necessary for a predetermined matrix calculation to be carried out. In order for the predetermined matrix calculation to be carried out, the parameter setting means 30 is provided. Basically, in the Von Kries&apos;s chromatic adaptation model, chromaticity coordinates (x, y, z) of the physiological primary colors of the human eyes (corresponding to the RGB primary colors of the CRT display device) and chromaticity coordinates (x, y, z) of the physiological white (corresponding to the white W of the CRT display device) are inputted as the characteristic values. Also, in this embodiment, the print formed by the DP is viewed under the CIE F8 fluorescent lamp (corresponding to a white point D50), and the white point of the NIFCRT is defined as D65. Therefore, the chromaticity of the white point D50 and the chromaticity of the white point D65 are also inputted as the characteristic values. The Von Kries&apos;s matrix calculation is thereby carried out.
Firstly, in cases where the chromaticity of the white point of the print formed by the DP is represented by (Xd50, Yd50, Zd50) and the chromaticity of the white point of the NIFCRT is represented by ((Xd65, Yd65, Zd65), the white points may be transformed into the LMS space with the physiological primary colors in accordance with Formulas (13) and (14) shown below. [ L M S ] = M &af; [ Xd50 Yd50 Zd50 ] ( 13 ) [ L ′ M ′ S ′ ] = M &af; [ Xd65 Yd65 Zd65 ] ( 14 )
In the formulas, (L, M, S) represents the results of the transformation of the chromaticity of the white point of the print into the LMS space with the physiological primary colors. Also, (L′, M′, S′) represents the results of the transformation of the chromaticity of the white point of the NIFCRT into the LMS space with the physiological primary colors. The matrix M is determined by the three physiological primary colors of the human eyes and the white point associated with the balance of the physiological primary colors.
The relationship between (L, M, S) and (L′, M′, S′) may be represented by Formula (15) shown below. [ L ′ M ′ S ′ ] = D &af; [ L M S ] wherein D = [ Ld65 Ld50 0 0 0 Md65 Md50 0 0 0 Sd65 Sd50 ]
Therefore, from Formulas (13), (14), and (15) shown above, the relationship between the chromaticity (Xd50, Yd50, Zd50) of the white point of the print formed by the DP and the chromaticity ((Xd65, Yd65, Zd65) of the white point of the NIFCRT may be represented by Formula (16) shown below. [ Xd65 Yd65 Zd65 ] = M &CenterDot; D &CenterDot; M - 1 &af; [ Xd50 Yd50 Zd50 ] ( 16 )
As for the physiological primary colors of the human eyes, several techniques have been proposed. In this embodiment, a technique, which was proposed by Estevez in 1979, is employed. The chromaticity coordinates of the physiological primary colors and the results of calculations of the transformation matrices to the LMS space, which are obtained when D65 and Se (the equi-energy white) are used for the physiological white, are shown below. L &af; ( 0.8374 0.1626 ) M &af; ( 2.3021 1.3021 ) S &af; ( 0.1669 0.0000 ) White : D65 &it; &NewLine; [ 0.40024 0.70760 - 0.08081 &it; - 0.22630 1.16532 0.04570 &it; 0.00000 0.00000 0.981822 ] White : Se &it; &NewLine; [ 0.38971 0.68898 - 0.07868 &it; - 0.22981 1.18340 0.04641 &it; 0.00000 0.00000 1.000000 ]
As for the physiological white, in cases where either one of the transformation matrices shown above is used, the matrix M.D.M−1 may be represented by Formula (17) shown below. V = M &CenterDot; D &CenterDot; M - 1 = [ &it; 0.9845 - 0.0547 0.0678 - 0.060 &it; 1.0048 0.0012 0.0000 0.0000 1.3200 ] ( 17 )
The transformation with the Von Kries&apos;s chromatic adaptation model is carried out by using the thus obtained matrix V. In cases where the transformation is to be carried out in the reverse direction, an inverse matrix V−1 of the matrix V is calculated, and the transformation is carried out by using the inverse matrix V−1.
The color transformation table forming apparatus in accordance with the present invention is not limited to the use of the Von Kries&apos;s chromatic adaptation model, and any of other chromatic adaptation models may be utilized. In such cases, predetermined parameters corresponding to the utilized adaptation model may be set by the parameter setting device 30.
In cases where the white ground of the print is taken as the reference white, the dynamic range of the DP is such that the brightness L*&equals;approximately 5 to 100.0. In cases where the white of the CRT display device is taken as the reference white, the dynamic range of the NIFCRT is such that the brightness L*&equals;0.0 to 100.0 as specified by the definition formula. Therefore, when the L*a*b* matching with the L*a*b* model is carried out, the black (R, G, B)&equals;(0, 0, 0) of the print formed by the DP is transformed into (R, G, B)&equals;(15, 16, 21) of the NIFCRT. Actually, when the CRT display device is viewed in a dark room, the black of the CRT display device has a certain level of brightness due to a dark current of the CRT display device. Also, in the viewing environment of the NIFCRT, 1% of the CRT&apos;s white is reflected from the tube surface. Therefore, brightness of approximately L*&equals;9 is possessed. Accordingly, actually, it is necessary for the black of the NIFCRT to be set to be lower than (0, 0, 0). For such purposes, besides the use of the defined NIFCRT formula, processing should be carried out such that the entire dynamic range of the CRT display device can be utilized as much as possible.
Since the aforesaid Von Kries&apos;s chromatic adaptation model is used, the white (R, G, B)&equals;(255, 255, 255) of the print formed by the DP is reliably transformed into the white (R, G, B)&equals;(255, 255, 255) of the NIFCRT. Therefore, as for the white in the dynamic range, no problems occur. Effects of tube surface reflection of the CRT display device bring about visual changes such that the black may float and the gradation at the shadow alone may become laid flat. Therefore, processing for raising the gradation is carried out such that the entire dynamic range of the CRT display device can be utilized as much as possible. FIG. 13 shows the calculations of the transformation range of the dynamic range for raising the gradation. Firstly, in a step S1, the black (R, G, B)&equals;(0, 0, 0) of the print is transformed by using the non-self-luminous direct transformation table LUT1, which has been calculated-in the manner described above. Also, in a step S2, black color L*a*b* signals (L0*, a0*, b0*), which have been transformed with the Von Kries&apos;s chromatic adaptation model, are obtained. Thereafter, in a step S3, the L*a*b* signals (L0*, a0*, b0*) are transformed in accordance with the self-luminous inverse transformation table LUT4, and the values of the black color of the print are thereby transformed into the values of the black color of the NIFCRT. Further, in a step S4, a judgment is made as to whether the thus obtained values fall or do not fall within the color reproduction range. In cases where it has been judged that the values fall within the color reproduction range, the aforesaid L*a*b* signals (L0*, a0*, b0*) are obtained as signals (L1*, a1*, b1*). In cases where it has been judged that the values do not fall within the color reproduction range, in a step S5, a0* and b0* are kept at the same values, &Dgr;L* is subtracted from L0*, and the value of L0* is thereby adjusted. In this case, in order for the limit of the raising of the gradation without the DP gray balance being changed, a0* and b0* are kept at the same values. The processing of the steps S3, S4, and S5 is repeated until, in the step S4, it is judged that the values fall within the color reproduction range. In this manner, the values (L1*, a1*, b1*) of the L*a*b* signals (L0*, a0*, b0*) are obtained.
L*&equals;(L*w1−L1*)/L*w0−L0*)×(L*−L0*)&plus;L1* (18)
wherein L* represents the transformation range information. In Formula (18) shown above, the white is transformed from L*w0 into L*w1 (actually, L*w0&equals;L*w1). In such cases, instead of L* being used, Y may be used as the transformation range information.
Thereafter, the dynamic range compensation is carried out for transforming the dynamic range of the DP image signals into the dynamic range of the NIFCRT image signals in accordance with the non-self-luminous direct transformation table LUT1, which has been obtained in the manner described above. Also, the color transformation is carried out for transforming the RGB signals for the DP into the RGB signals for the NIFCRT in accordance with the chromatic adaptation model (in this embodiment, the Von Kries&apos;s chromatic adaptation model) such that the appearances of the perceived colors may become identical between the image displayed on the DP and the image displayed on the NIFCRT.
Specifically, in this embodiment, the dynamic range compensation and the color transformation are carried out in the manner described below. Firstly, with respect to each lattice point, the RGB signals capable of being displayed on the DP are transformed into the XYZ signals. Thereafter, the signal transformation in accordance with the Von Kries&apos;s chromatic adaptation model is carried out in accordance with the Von Kries&apos;s matrix, which has been obtained previously. Also, the dynamic range compensation of the XYZ signals is carried out in accordance with the transformation range information, which has been obtained previously. Finally, the XYZ signals are transformed into the RGB signals for the NIFCRT in accordance with the self-luminous inverse transformation table LUT4. The information representing the correspondence relationship between the RGB signals capable of being displayed on the DP and the RGB signals for the NIFCRT, which have been calculated in the manner described above, is stored in the form of an LUT in the storage device 70. In this manner, the color direct transformation table 110 is formed.
Basically, the color inverse transformation table may be formed in the same manner as that for the color direct transformation table, except that the direction of signal transformation is reverse. Specifically, the dynamic range inverse compensation is carried out for transforming the dynamic range of the RGB signals for the NIFCRT into the dynamic range of the RGB signals for the DP in accordance with the self-luminous direct transformation table LUT3. Also, the color inverse transformation is carried out for transforming the RGB signals for the NIFCRT into the RGB signals for the DP in accordance with the chromatic adaptation model (in this embodiment, the Von Kries&apos;s chromatic adaptation model) such that the appearances of the perceived colors may become identical between the image displayed on the NIFCRT and the image displayed on the DP. The dynamic range inverse compensation and the color inverse transformation, which are carried out in this embodiment, will be briefly described hereinbelow.
Firstly, in order for the signal transformation to be carried out in accordance with the Von Kries&apos;s chromatic adaptation model, the inverse matrix of the aforesaid Von Kries&apos;s matrix is calculated by the calculation device. In such cases, the same parameters as those used in the calculation of the Von Kries&apos;s matrix may be used. Alternatively, instead of the parameters being set, only the information representing the Von Kries&apos;s matrix may be received, and the inverse matrix may be calculated directly.
Thereafter, with respect to each lattice point, the RGB signals capable of being displayed on the NIFCRT are transformed into the XYZ signals. Also, the dynamic range inverse compensation is carried out on the thus obtained XYZ signals in accordance with the transformation range information, which has been obtained previously. (In the dynamic range inverse compensation, the same technique as that for the aforesaid dynamic range compensation may be employed. However, the transformation range information is represented by a formula, which is obtained by solving Formula (18) shown above for L* in the right term.) Further, the signal transformation in accordance with the Von Kries&apos;s chromatic adaptation model is carried out in accordance with the Von Kries&apos;s inverse matrix, which has been obtained previously. (At this stage, the signals are still the XYZ signals.) Finally, the XYZ signals are transformed into the RGB signals for the DP in accordance with the non-self-luminous inverse transformation table LUT2. The information representing the correspondence relationship between the RGB signals capable of being displayed on the NIFCRT and the RGB signals for the DP, which have been calculated in the manner described above, is stored in the form of an LUT in the storage device 72. In this manner, a color inverse transformation table 210 is formed.
In the manner described above, when the color inverse transformation table is formed, the dynamic range inverse compensation is carried out by using the same transformation range information as the transformation range information used in the formation of the color direct transformation table. Also, the signal transformation is carried out in accordance with the Von Kries&apos;s chromatic adaptation model based upon the same parameters. Therefore, in cases where the original image signals for the DP are transformed into the image signals for the NIFCRT, and the thus obtained image signals for the NIFCRT are transformed to the image signals for the DP, the original image signals for the DP and the image signals for the DP, which have finally been transformed from the image signals for the NIFCRT, become identical with each other. Thus a failure in image signals, which will otherwise often occur from signal transformation, does not occur.
In the aforesaid embodiment, the non-self-luminous direct transformation relationship, the non-self-luminous inverse transformation relationship, the self-luminous direct transformation relationship, and the self-luminous inverse transformation relationship are set in the form of LUT&apos;S. However , the above-enumerated relationships need not necessarily take on the form of LUT Is and may take on the form of predetermined functions, or the like.
1. A method of forming a color transformation look-up table, comprising:
i) calculating a first correspondence relationship for a first transformation of color signals, which are capable of being reproduced on a non-self-luminous displaying medium, from first colorimetric system signals into second colorimetric system signals,
ii) calculating a second correspondence relationship for a second transformation of color signals, which are capable of being reproduced on a self-luminous displaying medium, from the second colorimetric system signals into the first colorimetric system signals,
iii) carrying out dynamic range compensation for transforming the dynamic range of the color signals, which are capable of being reproduced on the non-self-luminous displaying medium, into the dynamic range of the color signals, which are capable of being reproduced on the self-luminous displaying medium, in accordance with said first correspondence relationship and said second correspondence relationship, the transforming being carried out for the respective color signals, which are capable of being reproduced on the non-self-luminous displaying medium,
iv) carrying out color transformation for transforming the color signals, which are capable of being reproduced on the non-self-luminous displaying medium, into the color signals, which are capable of being reproduced on the self-luminous displaying medium, in accordance with a chromatic adaptation model such that the appearances of perceived colors may become identical between the image displayed on the non-self-luminous displaying medium, and
v) storing the color signals, which are capable of being reproduced on the non-self-luminous displaying medium, and the corresponding color signals capable of being reproduced on the self-luminous displaying medium, which have been obtained from said dynamic range compensation and said color transformation.
2. The method of forming a color transformation look-up table as in claim 1 wherein said color transformation comprises:
a) carrying out direct transformation of the first calorimetric system signals of the color signals, which are capable of being reproduced on the non-self-luminous displaying medium, into the second calorimetric system signals, said direct transformation being carried out in accordance with said first correspondence relationship,
b) carrying out chromatic adaptation transformation in accordance with the chromatic adaptation model on the second calorimetric system signals, which have been obtained from said direct transformation, and
c) carrying out inverse transformation of the signals, which have been obtained from said chromatic adaptation transformation, into the first colorimetric system signals, said inverse transformation being carried out in accordance with said second correspondence relationship.
3. The method of forming a color transformation look-up table as in claim 2 wherein said color transformation comprises:
a) forming transformation range information in accordance with said first correspondence relationship and said second correspondence relationship, and
b) transforming the signals, which have been obtained from said chromatic adaptation transformation or said direct transformation, in accordance with said transformation range information and between said chromatic adaptation transformation and said inverse transformation or between said direct transformation and said chromatic adaptation transformation.
4. The method of forming a color transformation look-up table as in claim 1 wherein said first correspondence relationship is calculated with a technique for estimating signals outside a color reproduction range and with an inverse transformation operation, which utilizes a Newton-Raphson technique.
i) a first calculator adapted to calculate a first correspondence relationship for transformation of color signals, which are capable of being reproduced on a non-self-luminous displaying medium, from first calorimetric system signals into second calorimetric system signals,
ii) a second calculator adapted to calculate second correspondence relationship for transformation of color signals, which are capable of being reproduced on a self-luminous displaying medium, from the second colorimetric system signals into the first colorimetric system signals,
iii) a dynamic range compensating function for carrying out dynamic range compensation for a compensating transformation of a dynamic range of the color signals, which are capable of being reproduced on the non-self-luminous displaying medium, into the dynamic range of the color signals, which are capable of being reproduced on the self-luminous displaying medium, in accordance with said first correspondence relationship and said second correspondence relationship, the compensating transformation being carried out for the color signals, which are capable of being reproduced on the non-self-luminous displaying medium,
iv) a color transforming function adapted to carry out color transformation for transforming the color signals, which are capable of being reproduced on the non-self-luminous displaying medium, into the color signals, which are capable of being reproduced on the self-luminous displaying medium, in accordance with a chromatic adaptation model such that the appearances of perceived colors may become identical between an image displayed on the self-luminous displaying medium and the image displayed on the non-self-luminous displaying medium, and
v) a storage unit for storing the color signals, which are capable of being reproduced on the non-self-luminous displaying medium, and the corresponding color signals capable of being reproduced on the self-luminous displaying medium, which have been obtained from said dynamic range compensation and said color transformation.
8. The apparatus for forming a color transformation look-up table as in claim 7 wherein said color transforming function comprises:
a) a direct transformation function adapted to carry out direct transformation of the first colorimetrics system signals of the color signals, which are capable of being reproduced on the non-self-luminous displaying medium, into the second colorimetric system signals, said direct transformation being carried out in accordance with said first correspondence relationship,
b) a chromatic adaptation transformation function adapted to carry out chromatic adaptation transformation in accordance with the chromatic adaptation model on the second colorimetric system signals, which have been obtained from said direct transformation, and
c) an inverse transformation function adapted to carry out inverse transformation of the second colorimetric system signals, which have been obtained from said chromatic adaptation transformation, into the first colorimetric system signals, said inverse transformation being carried out in accordance with said second correspondence relationship.
9. The apparatus for forming a color transformation look-up table as in claim 8 wherein said dynamic range compensating function comprises a transformation range information forming device adapted to form transformation range information in accordance with said first correspondence relationship and said second correspondence relationship, and
said dynamic range compensating function is adapted to transform the signals, which have been obtained from said chromatic adaptation transformation or said direct transformation, in accordance with said transformation range information and between said chromatic adaptation transformation and said inverse transformation or between said direct transformation and said chromatic adaptation transformation.
10. The apparatus for forming a color transformation look-up table as in claim 7 wherein said first calculator comprises an estimator adapted to estimate signals outside a color reproduction range and an inverse transformation operation function, which utilizes a Newton-Raphson technique.
i) calculating a first correspondence relationship for transformation of color signals, which are capable of being reproduced on a self-luminous displaying medium, from first colorimetric system signals into second colorimetric system signals,
ii) calculating a second correspondence relationship for transformation of color signals, which are capable of being reproduced on a non-self-luminous displaying medium, from the second calorimetric system signals into the first calorimetric system signals,
iii) carrying out dynamic range compensation for a compensation transformation of a dynamic range of the color signals, which are capable of being reproduced on the self-luminous displaying medium, into a dynamic range of the color signals, which are capable of being reproduced on the non-self-luminous displaying medium, in accordance with said first correspondence relationship and said second correspondence relationship, the compensation transformation being carried out for the color signals, which are capable of being reproduced on the self-luminous displaying medium,
iv) carrying out color transformation for transforming the color signals, which are capable of being reproduced on the self-luminous displaying medium, into the color signals, which are capable of being reproduced on the non-self-luminous displaying medium, in accordance with a chromatic adaptation model such that the appearances of perceived colors may become identical between the image displayed on the non-self-luminous displaying medium and an image displayed on the self-luminous displaying medium, and
v) storing the color signals, which are capable of being reproduced on the self-luminous displaying medium, and the corresponding color signals capable of being reproduced on the non-self-luminous displaying medium, which have been obtained from said dynamic range compensation and said color transformation.
13. The method of forming a color transformation look-up table as in claim 12 wherein said color transformation comprises:
a) carrying out direct transformation of the first colorimetric system signals of the color signals, which are capable of being reproduced on the self-luminous displaying medium, into the second colorimetric system signals, said direct transformation being carried out in accordance with said first correspondence relationship,
b) carrying out chromatic adaptation transformation in accordance with the chromatic adaptation model on the second colorimetric system signals, which have been obtained from said direct transformation, and
c) carrying out inverse transformation of the signals, which have been obtained from said chromatic adaptation transformation, into the first calorimetric system signals, said inverse transformation being carried out in accordance with said second correspondence relationship.
14. The method of forming a color transformation look-up table as in claim 13 wherein said dynamic range compensation comprises:
15. A method of forming a color transformation look-up table as defined in claim 12 wherein said first correspondence relationship is calculated with a technique for estimating signals outside a color reproduction range and with an inverse transformation operation, which utilizes a Newton-Raphson technique.
i) a first calculator adapted to calculate a first correspondence relationship for transformation of color signals, which are capable of being reproduced on the self-luminous displaying medium, from first colorimetric system signals into second colorimetric system signals,
ii) a second calculator adapted to calculate second correspondence relationship for transformation of color signals, which are capable of being reproduced on a non-self-luminous displaying medium, from the second colorimetric system signals into the first colorimetric system signals,
iii) a dynamic range compensating function for carrying out a dynamic range compensation transformation of a dynamic range of the color signals, which are capable of being reproduced on the self-luminous displaying medium, into a dynamic range of the color signals, which are capable of being reproduced on the non-self-luminous displaying medium, in accordance with said first correspondence relationship and said second correspondence relationship, the compensation transformation being carried out for the color signals, which are capable of being reproduced on the self-luminous displaying medium,
iv) a color transforming function adapted to perform color transformation of the color signals, which are capable of being reproduced on the self-luminous displaying medium, into the color signals, which are capable of being reproduced on the non-self-luminous displaying medium, in accordance with a chromatic adaptation model such that the appearances of perceived colors may become identical between the image displayed on the non-self-luminous displaying medium and the image displayed on the self-luminous displaying medium, and
v) a storage unit for storing the color signals, which are capable of being reproduced on the self-luminous displaying medium, and the corresponding color signals capable of being reproduced on the non-self-luminous displaying medium, which have been obtained from said dynamic range compensation and said color transformation.
19. The apparatus for forming a color transformation look-up table as in claim 18 wherein said color transforming function comprises:
a) a direct transformation function adapted to perform direct transformation of the first colorimetric system signals of the color signals, which are capable of being reproduced on the self-luminous displaying medium, into the second colorimetric system signals, said direct transformation being carried out in accordance with said first correspondence relationship,
b) a chromatic adaptation transformation function for carrying out chromatic adaptation transformation in accordance with a chromatic adaptation model on the second colorimetric system signals, which have been obtained from said direct transformation, and
c) an inverse transformation function for carrying out inverse transformation of the signals, which have been obtained from said chromatic adaptation transformation, into the first colorimetric system signals, said inverse transformation being carried out in accordance with said second correspondence relationship.
20. The apparatus for forming a color transformation look-up table as in claim 19 wherein said dynamic range compensating function comprises a transformation range information forming unit for forming transformation range information in accordance with said first correspondence relationship and said second correspondence relationship, and
21. The apparatus for forming a color transformation look-up table as in claim 18 wherein said first calculator comprises an estimator adapted to estimate signals outside a color reproduction range and an inverse transformation operation function, which utilizes a Newton-Raphson technique.
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Assignee: Fuji Photo Film Co., Ltd. (Minamiashigara)
Application Number: 09/163,430