JP5888488B2 - Color conversion apparatus and color conversion processing program - Google Patents

Description

  The present invention relates to a color conversion device and a color conversion processing program.

  When predicting a color output from an output device such as a printing press or a color image forming device, based on a pair of a color value given to the output device and a colorimetric value obtained by measuring the color output from the output device. In general, prediction is performed using interpolation or a color prediction model. As the color prediction model, an experimental model using an actual measurement value such as a model using a neural network described in Patent Document 1 or a model using weighted regression described in Patent Document 2 is used. Has been.

  On the other hand, there is a method using a theoretical model as another color prediction method. As a theoretical model, a Neugebauer model is common. In the Neugebauer model, for each color material used when the output device outputs colors, a combination of 0% and 100% is given to the output device as a reference color, and the color output from the output device Measure the color. The color output from the output device is predicted from the colorimetric value and the area ratio of each color material corresponding to the color value given as the processing target.

  As a model applying the Neugebauer model, there is a cellular Neugebauer model. The cellular Neugebauer model divides the area between the reference colors of the Neugebauer model into several parts, sets the reference color for each area (cell), obtains the colorimetric value, The Neugebauer model is applied to this.

  The Neugebauer model is, for example, a color image forming apparatus that reproduces colors using four color materials of C (cyan), M (magenta), Y (yellow), and K (black). Colorimetric values for 16 reference colors ranging from primary colors reproduced with maximum use of one color material to quaternary colors reproduced with maximum use of four color materials Is required.

  However, in color image forming apparatuses, the amount of color material (for example, toner or ink) used when outputting an image may be limited. For example, in an electrophotographic color image forming apparatus using toner, the amount of color material used is limited due to restrictions on various conditions such as image output speed, toner characteristics, and fixing device performance. Also, in a liquid jet type color image forming apparatus using ink, the amount of color material used is limited due to restrictions on various conditions such as image output speed, ink characteristics, and water absorption characteristics of paper.

  In this way, when the usage amount of the color material used in the color image forming apparatus is limited (total amount limitation), the usage amount of the color material may be larger than the total amount limit value in the reference color. . For such a reference color, a colorimetric value is not acquired because it is not output from the apparatus, and therefore a Neugebauer model is not constructed.

  For example, in Patent Document 3, a colorimetric value corresponding to a reference color whose total color material amount is larger than the total amount limit value is estimated using a colorimetric value within the total amount limit value, and the colorimetric values corresponding to the reference color are aligned. Describes a method for predicting reproduced colors using a cellular Neugebauer model. In this method, since the color reproduction characteristics of the color image forming apparatus are nonlinear, the colorimetric value corresponding to the reference color larger than the estimated total amount limit value includes an error, and the reproduction color predicted by the model is also It will contain errors.

Japanese Unexamined Patent Publication No. 7-87347 JP-A-10-262157 JP 2009-130842 A

  The present invention provides a color conversion apparatus and a color conversion process capable of predicting an output color signal with higher accuracy than when the configuration is not provided even when a limit is imposed on the amount of color material used in the output apparatus. The purpose is to provide a program.

  According to the first aspect of the present invention, the total amount corresponding to the reference color for a reference color that does not satisfy the total amount limit value that is the upper limit of the sum of the values of the color components among the reference colors used in the theoretical color prediction model. A correction means for obtaining a corrected color signal by correcting a processing target color signal given by a correction function for correcting a color satisfying a limit value as the reference color or toward the reference color, and the reference color and the colorimetric value For the reference color that does not satisfy the total amount limit value among the pairs, the theoretical color prediction model using the colorimetric values obtained for the color that satisfies the corresponding total amount limit value as a pair, from the corrected color signal It is a color conversion apparatus characterized by having a prediction means for predicting an output color signal.

  The invention described in claim 2 of the present application is a plurality of colors in which the correction means in the invention described in claim 1 of the present application changes a certain color component and fixes other color components for each color component. A one-dimensional correction obtained from a change in the colorimetric value obtained from the colorimetric value obtained by obtaining a colorimetric value for the color that has been changed in the color space so as to satisfy the total amount limit value for the color that does not satisfy the total amount limit value. The color conversion apparatus is characterized by performing correction using a function.

  In the invention described in claim 3 of the present application, the correction means in the invention described in claim 2 of the present application obtains the correction function corresponding to each value obtained by fixing other color components for each color component, The color conversion device is characterized in that the correction function is selected according to a value of a fixed color component, and the corresponding color component is corrected.

  According to a fourth aspect of the present invention, the correction means according to any one of the first to third aspects of the present invention is such that the sum of the color components of the processing target color signal satisfies the total amount limit value. Correction using the correction function, and when the sum of the color components of the color signal to be processed exceeds the total amount limit value, the color is corrected by a method different from the correction by the correction function It is a conversion device.

  The invention according to claim 5 of the present application is a color conversion processing program for causing a computer to execute the function of the color conversion apparatus according to any one of claims 1 to 4. .

  According to the invention described in claim 1 of the present application, even when the total amount of color material is restricted in the output device, it is possible to predict the output color signal with higher accuracy than in the case where this configuration is not provided. effective.

  According to the second aspect of the present invention, it is possible to predict the output color signal with higher accuracy than in the case where the present configuration is not provided.

  According to the third aspect of the present invention, the output color signal can be predicted with high accuracy even when the total amount restriction is imposed more easily than in the case where the present configuration is not provided.

  According to the fourth aspect of the present invention, it is possible to predict the output color signal with high accuracy even when the total amount restriction is imposed more easily than in the case where the present configuration is not provided.

  According to the invention of claim 5 of the present application, the effect of the invention of any one of claims 1 to 4 can be obtained.

It is a block diagram which shows the 1st Embodiment of this invention. It is explanatory drawing of an example of the structure which acquires the pair of a reference value and a colorimetric value. It is explanatory drawing of an example of the process of the total amount restriction | limiting with respect to a reference color. It is explanatory drawing of the 1st example of the correction function used in the color signal correction | amendment part. It is explanatory drawing of the 2nd example of the correction function used in the color signal correction | amendment part. It is explanatory drawing of an example of the correction process by the 2nd example of a correction function. It is explanatory drawing of an example of the structure which calculates a correction function in the 3rd example of a correction function. It is explanatory drawing of an example of the process of the total amount restriction | limiting with respect to the gradation color at the time of calculating a correction function. It is explanatory drawing of an example of the change of the value of a color component, and the change of a colorimetric value. It is explanatory drawing of an example of the correction function obtained in the 3rd example of a correction function. It is explanatory drawing of an example of the correction process by a correction function. It is explanatory drawing of an example of prediction of an output color signal. It is a block diagram which shows the 2nd Embodiment of this invention. It is explanatory drawing of an example of the conversion method when exceeding the total amount limit value in the 2nd Embodiment of this invention. It is explanatory drawing of another example of the conversion method when exceeding the total amount limit value in the 2nd Embodiment of this invention. FIG. 15 is an explanatory diagram of an example of a computer program, a storage medium storing the computer program, and a computer when the functions described in the embodiments of the present invention are realized by the computer program.

  FIG. 1 is a block diagram showing a first embodiment of the present invention. In the figure, 11 is a color signal correction unit, and 12 is an output color signal prediction unit.

  The color signal correction unit 11 corrects the processing target color signal with a correction function to obtain a corrected color signal. Here, correction is performed for each color component of the color signal to be processed. The output color signal prediction unit 12 to be described later predicts an output color signal using a theoretical color prediction model, and among the reference colors used when constructing the theoretical color prediction model, the sum of the values of the color components. For a reference color that does not satisfy the total amount limit value that is the upper limit of the color, a colorimetric value obtained with a color that satisfies the total amount limit value corresponding to the reference color is used as the colorimetric value of the reference color. In this case, since the colorimetric value is not the colorimetric value of the reference color, a correction function that uses the color that satisfies the total amount limit value given to the output device to obtain the colorimetric value as the reference color, or the color as the reference color The color signal to be processed is corrected in advance using a correction function that corrects for As the correction function, at least a color that satisfies the total amount limit value corresponding to the reference color is used as the reference color, or any function that corrects toward the reference color, such as an approximate expression or a weighted regression. It is preferable to make the relationship between the input value and the correction value smooth. An example of the correction function will be described later. A plurality of correction functions may be provided, and any one of them may be selected and used.

  The output color signal prediction unit 12 predicts an output color signal from the corrected color signal obtained by the color signal correction unit 11 using a theoretical color prediction model that uses a pair of a reference color and a colorimetric value. For a reference color that does not satisfy the total amount limit value, the colorimetric values obtained for the colors that satisfy the corresponding total amount limit value are paired.

  As an example, an output device that outputs an image using C, M, Y, and K color materials is assumed, and the processing target color signal is a color signal (c) in the CMYK color space having C, M, Y, and K as color components. , M, y, k), the output color signal to be predicted is a color signal (Xo, Yo, Zo) in the XYZ color space. Of course, it goes without saying that the color signal to be processed and the output color signal may be color signals in other color spaces.

  When the correction functions corresponding to the respective color components are fc, fm, fy, and fk, the color signal correcting unit 11 performs c → fc (c), m → fm (m), y → fy (y), k → fk (k) are corrected, and corrected color signals (fc (c), fm (m), fy (y), fk (k)) are obtained. obtain. An example of the correction function will be described later.

The output color signal prediction unit 12 uses a reference color (Cp, Mp, Yp, Kp) and colorimetric values (Xp, Yp, Zp) corresponding to the reference color, for example, using a Neugebauer halftone dot model. Output color signals (Xo, Yo, Zo) from corrected color signals (fc (c), fm (m), fy (y), fk (k)) obtained by correcting the color signal to be processed by the signal correction unit 11. Predict. The number of reference colors is 2 ^j (j = number of colors), and when 4 colors of C, M, Y, and K are used, 2 ⁴ = 16 colors.

For example, when the Neugebauer equation modified by Yule Nielsen is used as a model, the equation is as follows.
XYZo = [Σ _{i = 1} ¹⁶ w _i (fc (c), fm (m), fy (y), fk (k)) · XYZi ^{1 / n} ] ⁿ (1)

Here, XYZo is an output color signal, and XYZi is a colorimetric value corresponding to the i-th reference color. N is Yule Nielsen's n value for correcting the influence of optical dot gain (apparent dot area increase / lightness decrease due to light scattering in the paper). An appropriate value is obtained in advance. (Fc (c), fm (m), fy (y), fk (k)) are correction color signals. Here, fc (c), fm (m), fy (y), fk (k) Takes a value between 0 and 1. w _i is a halftone dot area ratio, which is a function of fc (c), fm (m), fy (y), and fk (k), and is obtained by the following equation.
w _w = (1-fc (c)). (1-fm (m)). (1-fy (y)). (1-fk (k))
_{w c = fc (c) ·} (1-fm (m)) · (1-fy (y)) · (1-fk (k))
w _m = (1-fc (c)). fm (m). (1-fy (y)). (1-fk (k))
_{w y = (1-fc (} c)) · (1-fm (m)) · fy (y) · (1-fk (k))
_{w k = (1-fc (} c)) · (1-fm (m)) · (1-fy (y)) · fk (k)
w _cm = fc (c) .fm (m). (1-fy (y)). (1-fk (k))
w _my = (1-fc (c)). fm (m) .fy (y). (1-fk (k))
w _cy = fc (c). (1-fm (m)). fy (y). (1-fk (k))
w _ck = fc (c). (1-fm (m)). (1-fy (y)). fk (k)
w _mk = (1-fc (c)). fm (m). (1-fy (y)). fk (k)
w _yk = (1−fc (c)) · (1−fm (m)) · fy (y) · fk (k)
w _cmy = fc (c) .fm (m) .fy (y). (1-fk (k))
w _cmk = fc (c) _.fm (m). (1-fy (y)). fk (k)
w _cyk = fc (c). (1-fm (m)). fy (y) .fk (k)
w _myk = (1−fc (c)) · fm (m) · fy (y) · fk (k)
w _cmyk = fc (c) .fm (m) .fy (y) .fk (k)

  The colorimetric value corresponding to the reference color is obtained by giving the reference color to the output device and measuring the color output from the output device. At this time, for the reference color that does not satisfy the total amount limit value, the colorimetric value obtained for the color that satisfies the corresponding total amount limit value is associated.

  FIG. 2 is an explanatory diagram of an example of a configuration for acquiring a reference value / colorimetric value pair. In the figure, 21 is a total amount limit value setting unit, 22 is a total amount limit unit, 23 is an output device, and 24 is a colorimetric unit. The output device 23 is an output device that is a target of color prediction. The total amount limit value setting unit 21 presets a total amount limit value determined based on the constraint condition of the output device 23.

  The total amount limiting unit 22 changes the value of each color component so that the sum of the values of the respective color components exceeds the total amount limiting value set in the total amount limiting value setting unit 21 so that it falls within the total amount limiting value. Thus, the color within the total amount limit value corresponding to the reference color outside the total amount limit value is obtained. For example, if the reference color is a color signal in the CMYK color space, K is fixed, C, M, and Y are maintained, and C, M, and Y are decreased so that the sum of CMYK is within the total amount limit value. . Of course, the value may be changed by other methods so as to be within the total amount limit value. In the case of other color spaces, the value may be changed so as to be within the total amount limit value by a method corresponding to the color space.

  The color after the value has been changed so that the reference color exceeding the total amount limit value is within the total amount limit value and the other reference colors within the total amount limit value are provided to the output device 23 and output from the output device 23. The color measurement unit 24 measures the color output from the output device 23 and obtains a color measurement value. The obtained colorimetric value is paired with a reference color that is the basis of the colorimetric value. At that time, the colorimetric value of the color whose value has been changed to be within the total amount limit value is paired with the reference color before the change.

  FIG. 3 is an explanatory diagram of an example of the total amount restriction process for the reference color. In FIG. 3, for the sake of simplicity, the total amount restriction processing for two colors C and M of the color components is shown. Both C and M take values from 0 to 100, and the total amount restriction value is expressed as follows. 100. The color that is the total amount limit value is indicated by a broken line.

  When C and M are used as the color components, the reference colors are white (denoted as W) where C = M = 0, cyan (denoted as C) where C = 100 and M = 0, C = 0, M = 100 Magenta (shown as M) and blue (shown as C + M) where C = M = 100. When the total amount limit value is 100, the total amount of C + M reference colors among the four reference colors is 200, which exceeds the total amount limit value. Therefore, the reference color is associated with a color that satisfies the total amount limit value. For example, the ratio of C and M is kept constant, and the values of C and M are decreased so that the sum is within the total amount limit value. Specifically, in this example, it is decreased to (C, M) = (100, 100) → (50, 50). In FIG. 3, for the C + M reference color, the color before change is indicated by a white circle, and the color after change is indicated by a black circle.

  In this way, the reference color that is outside the total amount limit value is given to the output device 23 the color changed so as to be within the total amount limit value, and other reference colors, and the color output from the output device 23 is measured. As a result, a pair of a reference color and a colorimetric value is obtained in the output device in which the total amount restriction is imposed. For the C + M reference color, not the color measurement value of the color of C = M = 100, but the color measurement value of the color of C = M = 50 is obtained and used as the color measurement value paired with the reference color of C + M.

  For the C + M reference color, a colorimetric value cannot be obtained if the color is C = M = 100 due to the total amount limitation. Therefore, a theoretical color prediction model such as the Neugebauer equation is not established, but it corresponds to the C + M reference color. If a colorimetric value is obtained for a color within the total amount limit value and the colorimetric value is a C + M colorimetric value, a theoretical color prediction model is established. However, for example, the Neugebauer equation is a formula that predicts a reproduction color from the colorimetric value of the color (reference color) of the combination of the lower limit value (for example, 0) and the upper limit value (for example, 100) of each color component and the area ratio of each color component. For this reason, if a colorimetric value of a color different from the reference color is substituted as it is due to the total amount restriction, the linear relationship is lost and a prediction error occurs. For example, an output color signal that is predicted even for a color that has obtained a colorimetric value is a color different from the colorimetric value. Therefore, before using a theoretical color prediction model such as the Neugebauer equation, the color signal to be processed is corrected and acquired with a color that satisfies the total amount limit value corresponding to the reference color that does not satisfy the total amount limit value. Even if the colorimetric value is used as it is as the colorimetric value for the reference color, the prediction error due to the influence of the total amount restriction is absorbed. Such correction processing is performed in the color signal correction unit 11.

  As described above, the correction function used in the color signal correction unit 11 uses, for the reference color that does not satisfy the total amount limit value, the colorimetric value acquired with the color that satisfies the total amount limit value corresponding to the reference color. Correction for use as a colorimetric value is performed. Therefore, the correction function is a function for correcting at least a color satisfying the total amount limit value corresponding to the reference color that does not satisfy the total amount limit value as the reference color, or correcting toward the reference color. Some examples of the correction function used in the color signal correction unit 11 will be described.

  FIG. 4 is an explanatory diagram of a first example of a correction function used in the color signal correction unit 11. In this example, the color region restricted by the total amount restriction is transformed into a color region in the case where the total amount restriction is not imposed. FIG. 4 also shows two color components C and M. Both C and M take values from 0 to 100, and the total amount limit value is 100. The color that is the total amount limit value is indicated by a broken line. In the case of this example, as described with reference to FIG. 3, (C, M) shown as C + M is a colorimetric value of a reference color of (100, 100), and (C, M) is (50, 50). Color prediction is performed by using a color measurement value of a color by a theoretical color prediction model. As correction processing for that purpose, in this example, correction processing is performed in which at least the color of (C, M) = (50, 50) becomes the reference color of (C, M) = (100, 100).

  More specifically, (C, M) is (0, 0), (100, 0), (50, 50), and (0, 100) is a color region connecting points (C, M) = A transformation that transforms the color region may be performed so that the color region connects the points (0, 0), (100, 0), (100, 100), and (0, 100). By this correction processing, for example, the color of the section of (C, M) = (100, 0) and (C, M) = (50, 50), which becomes the total amount limit value, is (C, M) = (100, 0). And (C, M) = (100,100), and the colors of (C, M) = (50,50) and (C, M) = (0,100) are (C , M) = (100, 100) and (C, M) = (0, 100), the colors are corrected respectively. For example, correction may be performed while maintaining the ratio of each color component. For the colors inside the total amount limit value, correction may be performed so that the correction amount in the total amount limit value decreases as the distance from the total amount limit value increases in the direction in which the ratio of the color components is maintained. In the example shown in FIG. 4, for some colors, the color before correction is indicated by a black circle, and the color after correction is indicated by a white circle.

  FIG. 5 is an explanatory diagram of a second example of the correction function used in the color signal correction unit 11. In the first example of the correction function described above, in order to perform correction in the color space, for example, a two-dimensional correction function is used in the two-dimensional color space shown in FIG. In the second example of the correction function, an example is shown in which correction processing is performed using a one-dimensional correction function that corrects each color component. FIG. 5A also shows two color components, C and M. Both C and M take values from 0 to 100, the total amount limit value is 100, and the color that is the total amount limit value is a broken line. Is shown.

  In FIG. 5A, considering the case where the value of M is fixed to 50, the total amount limit is satisfied when the value of C is 0 or more and 50 or less. A section that satisfies the total amount restriction is indicated by a bold line. Here, since the colorimetric values of (C, M) = (50,50) are used as the colorimetric values of the reference color of (C, M) = (100,100), (C, M Correction processing is performed in which the color of (M) = (50, 50) becomes the reference color of (C, M) = (100, 100). That is, the color of C = 50 when M = 50 is fixed may be corrected to C = 100. Then, when M = 50, a color having a C value of 0 or more and 50 or less may be corrected to a color of 0 or more and 100 or less.

  Such correction processing may be performed for other values of M. For example, for M = 25, a color having a C value of 0 or more and 75 or less may be corrected to a color of 0 or more and 100 or less, and for M = 75, a color having a C value of 0 or more and 25 or less may be corrected. Correct to color. When these are summarized, the function shown in FIG. Using these functions as correction functions, correction processing may be performed on C. Of course, correction processing is also performed for M using a correction function for M.

  In the correction function in this example, the color component for which the correction function is to be obtained is made variable, and other color components are fixed, so that the color range of the color component made variable from the total amount limit value is determined. Further, since the corrected color range is determined from the color components of the reference color, a variable color component correction function can be obtained with a fixed color component value. Such a correction function may be acquired by changing the value of the fixed color component. Further, a correction function may be acquired as a color component that makes each color component variable in order.

  FIG. 6 is an explanatory diagram of an example of correction processing according to the second example of the correction function. FIG. 6 shows an example of the relationship between the color signal to be processed and the correction color signal when the second example of the correction function shown in FIG. 5 is used. When the correction function is obtained for each of C and M by the method described with reference to FIG. 5, for example, the processing target color signal indicated by a black circle in FIG. 6 is corrected to the correction color signal indicated by a white circle. . As described above, in the correction in this example, for the reference color of C = M = 100, the colorimetric value obtained with the color of C = M = 50 that satisfies the total amount limit value is the original reference color of C = M = 100. This is due to the fact that the colorimetric value is set to.

  For example, if the processing target color signal is C = M = 50, basically, the colorimetric value corresponding to the processing target color signal is predicted by correcting C = M = 100. For the reference color of C = M = 100, the colorimetric value obtained with the color of C = M = 50 that satisfies the total amount limit value is used as the colorimetric value of the original reference color of C = M = 100. It is because.

  If the processing target color signal is C = 25 and M = 50, the correction is basically made to C = 50 and M = 67. The range of C when M = 50 is fixed is 0 or more and 50 or less, and C = 25 of the color signal to be processed corresponds to a half position. Since the colorimetric value at C = 50 is the colorimetric value at C = 100, the half position corresponds to the C = 50 position of the correction color signal from the colorimetric value. Further, when the range of M is viewed with C = 25 fixed, it is 0 or more and 75 or less, and M = 50 corresponds to a position of 2/3. Since the colorimetric value of M = 50 is the colorimetric value of M = 100, the position of 2/3 corresponds to the position of M = 67 of the correction color signal from the colorimetric value.

  Next, a third example of the correction function used in the color signal correction unit 11 will be described. When color prediction is performed using a theoretical color prediction model, correction using colorimetric values is performed for each color component in order to correct non-linearity of the color space. In the third example of the correction function, An example is shown in which correction using this colorimetric value is also performed when a total amount restriction is imposed.

  When correcting the nonlinearity of the color space, make one color component variable, fix other color components, obtain colorimetric values while changing the value of the variable color components, and change the correction function from that relationship The correction processing is performed. However, when a total amount limit is imposed, a colorimetric value cannot be obtained for colors exceeding the total amount limit. Therefore, for the color that does not satisfy the total amount limit value by changing the variable color component value, the colorimetric value of the color changed in the color space so as to satisfy the total amount limit value is obtained. From the obtained colorimetric value change, a one-dimensional correction function is obtained when other color components in the variable color component are fixed. A correction function is obtained for each combination of values of other color components. Further, such a correction function is obtained as a color component in which each color component is variable. Hereinafter, this method will be described in detail.

  FIG. 7 is an explanatory diagram of an example of a configuration for calculating the correction function in the third example of the correction function. In the figure, 31 is a correction function calculation unit. The total amount limiting value setting unit 21, the total amount limiting unit 22, the output device 23, and the color measurement unit 24 have the configurations described in FIG. 2, but when calculating the correction function, the color component of one color that is variable is changed. For the other color components, a plurality of fixed color signals are given to the total amount limiting unit 22, and corresponding colorimetric values are obtained by the colorimetric unit 24. At this time, the color that does not satisfy the total amount limit value is changed in the color space so as to satisfy the total amount limit value, and the colorimetric value corresponding to the changed color is obtained by the color measurement unit 24.

  The correction function calculation unit 31 calculates a correction function from this colorimetric value. This correction function is obtained from a pair of a color given from the total amount limiting unit 22 to the output device 23 and a colorimetric value obtained by the colorimetric unit 24, and may be any function. Will be described later.

  FIG. 8 is an explanatory diagram of an example of a total amount restriction process for gradation colors when calculating a correction function. In FIG. 8, for the sake of simplicity, the total amount restriction process for two colors C and M of the color components is shown. Both C and M take values from 0 to 100, and the total amount restriction value is expressed as follows. 100. The color that is the total amount limit value is indicated by a broken line. Here, description will be made assuming that a correction function for C is calculated.

  FIG. 8 shows a case where the value of M is fixed to 0, 50, 100, and the value of C is changed to 0, 25, 50, 75, 100 for each M value. Since the total amount limit value is 100, when the value of C is changed with M = 0, the total amount is within the total amount limit value for any color and is used as it is. However, when M is fixed at M = 50 and the value of C is changed, the color C = 75,100 is changed. When M is fixed at M = 100 and the value of C is changed, C = 25,50, Each of the colors 75 and 100 exceeds the total amount limit value. Therefore, these colors are changed to colors that satisfy the total amount limit value. The change method may be any method, but here, as an example, the color is changed to a color that is reduced so that the sum is within the total amount limit value while maintaining the ratio of C and M. In FIG. 8, for each color exceeding the total amount limit value, the color before change is indicated by a white circle and the color after change is indicated by a black circle. In this way, a color signal that has been changed to a color that satisfies the total amount limit value for colors that exceed the total amount limit value is provided to the output device 23, and the color output from the output device 23 is measured to obtain a corresponding colorimetric value. .

  FIG. 9 is an explanatory diagram of an example of the change of the color component value and the change of the colorimetric value. FIG. 9 shows an example of changes in the X component of the colorimetric values XYZ obtained by changing the value of C for each case where the value of M is fixed at 0, 50, and 100. A case where M = 0 is fixed is indicated by a solid line, a case where M = 50 is fixed is indicated by a broken line, and a case where M = 100 is fixed is indicated by a dotted line. The example shown in FIG. 9B shows a case where a color exceeding the total amount limit value is changed to a color within the total amount limit value, output from the output device 23, and measured, and the total amount limit is shown as a comparative example. FIG. 9A shows a case in which color measurement is performed by outputting from the output device 23 without imposing the above.

  Referring to FIG. 9A, when no total amount restriction is imposed, the X component of the colorimetric value tends to decrease as the C value increases, apart from the reproduced image quality. On the other hand, when the total amount restriction is imposed, it can be seen from FIG. 9B that the change in the X component of the colorimetric value differs between the inside and outside of the total amount restriction value. For example, in the case of M = 50, the change in the X component is different from C = 50. This difference in change in the colorimetric value appears as an error in the predicted value based on the theoretical color prediction model. Therefore, in this third example, a correction function is calculated from the colorimetric values corresponding to the colors obtained by imposing a total amount restriction on the gradation color changed for C, and the given color signal to be processed is calculated. On the other hand, by correcting with a correction function, a prediction error in the case of using the colorimetric value of the reference color imposed with the total amount limitation is absorbed.

As the correction function, where f as an example ^{_{(cj) = (X cj 1}} / n -X c0 1 / n) / (X c100 1 / n -X c0 1 / n) ... (2)
The following function is used. This function f (cj) shows an example of a correction function for the C color component when the X component of the colorimetric value is used, and cj is the value of C among the color components of the color signal to be processed. It is supposed to be. Xcj shows the X component of the colorimetric values when the value of C is j, X _c100 is the X component when C is 100, X _c0 is the X component when C is 0, respectively ing. n is a predetermined value.

  FIG. 10 is an explanatory diagram of an example of a correction function obtained in the third example of the correction function. Also in FIG. 10, for each case where the value of M is fixed to 0, 50, 100, the relationship between the C value of the color signal to be processed and the C value of the corrected color signal corrected by the correction function f (cj). An example is shown. A case where M = 0 is fixed is indicated by a solid line, a case where M = 50 is fixed is indicated by a broken line, and a case where M = 100 is fixed is indicated by a dotted line. An example of the correction function f (cj) calculated from the colorimetric values shown in FIG. 9B is shown in FIG. 10B, and calculated from the colorimetric values shown in FIG. 9A for reference. An example of the correction function f (cj) to be performed is shown in FIG.

  When the total amount limitation shown in FIG. 9A is not imposed, the X component of the colorimetric value tends to decrease as the value of C increases, and the tendency does not depend on the value of M. As shown in (A), the correction function is a function that does not depend on the value of M. On the other hand, since the change tendency of the X component of the colorimetric value when the total amount restriction shown in FIG. 9B is imposed is different between the inside and outside of the total amount restriction value, the correction is performed as shown in FIG. 10B. The function depends on the value of M. For example, when M = 50, correction is performed so that the value of the C component of the correction color signal approaches 100 when the value of the C component of the processing target color signal is 50.

  That is, for the color of C = M = 100, which is one of the reference colors, the total amount limit value (here, the total amount limit value = 100) is not satisfied, and therefore the colorimetric value is calculated with the corresponding C = M = 50 color. Then, the color measurement value of the color of C = M = 50 is used as the color measurement value of the reference color of C = M = 100, and a theoretical color prediction model is applied. When a color of M = C = 50 is given as the color signal to be processed, basically, if the color signal is corrected to C = M = 100, the predicted value based on the theoretical color prediction model is a colorimetric value of C = M = 50. Will be obtained. Therefore, the correction is performed so that the value of C of the color signal to be processed is changed from 50 to 100 by the correction function in the case of M = 50.

  In the case of M = 0, the total amount is within the limit value regardless of the value of C. Therefore, the correction function is the same in FIGS. 10A and 10B. Further, in the case of M = 100, other than C = 0, it is outside the total amount limit value. In this case, although the change in the X component of the colorimetric value shown in FIG. 9B is different from the case where no total amount restriction is imposed, the decreasing tendency of the X component does not change with the change in C. The correction function tends to be linear with respect to the input value.

  FIG. 11 is an explanatory diagram of an example of a correction process using a correction function. FIG. 11 shows an example of the relationship between the processing target color signal and the correction color signal in the case shown in FIG. As described above, the C component is corrected using the expression (2). If the correction processing is also performed for the M component using such a correction function, for example, the processing target color signal indicated by a black circle in FIG. The correction color signals are indicated by white circles.

  For example, if the processing target color signal is C = M = 50, the correction is basically performed toward C = M = 100. If the color signal to be processed is C = 25 and M = 50, in this example, it is corrected to C = 50 and M = 75. Of course, these values are merely examples, and change depending on the colorimetric values. In the third example of the correction function, when Expression (2) is used as the correction function, a color outside the total amount limit value is changed to a color within the total amount limit value, and a colorimetric value is obtained to obtain the correction function. ing. Therefore, for example, in the example shown in FIG. 11, there is a case where a color of C = M = 50 that satisfies the total amount limit value corresponding to the reference color does not become C = M = 100, which is the reference color, by the correction function. Yes. However, since the correction function is obtained based on the colorimetric values, the accuracy of color prediction as a whole color space is improved compared to the first and second examples of the correction function described above. Further, in the second example of the correction function described above, the processing target color signal exceeding the total amount limit value is uniformly corrected to the reference color, but in the third example of this correction function, the total amount limit value is exceeded. In this case, the gradation is reflected in the correction color signal.

  As described in the above description, if the processing target color signal is a color signal in the CMYK color space, a correction function is obtained not only for C but also for M, Y, and K, and the processing target color signal is determined by the correction function. Correction is performed to obtain a corrected color signal, and an output color signal is predicted by a theoretical color prediction model. When obtaining the correction function, for example, the C correction function gives an output device a color signal in which the values of C are changed while fixing the values of M, Y, and K, and the output color is measured to measure color. As shown in FIG. 9, a change in the colorimetric value is obtained, and for example, a correction function may be obtained by equation (2). For the M correction function, a color signal in which the values of C, Y, and K are fixed and the value of M is changed is given to the output device, the output color is measured, and the correction function is calculated from the colorimetric values. Find it. For the Y correction function, a color signal in which the value of C, M, and K is fixed and the value of Y is changed is given to the output device, the output color is measured, and the correction function can be obtained from the colorimetric value. That's fine. As for the correction function of K, a color signal obtained by changing the value of K with the C, M, and Y values fixed can be given to the output device, the output color can be measured, and the correction function can be obtained from the colorimetric values. That's fine. The step size for changing each color component is not limited to the above example, but may be determined in advance and may not be equal. Further, the step size of the value to be fixed is not limited to the above example, but may be determined in advance and may not be equal.

  For each color component, a correction function is obtained for each value with the other color components fixed. Select one of the fixed color component values of the processing target color signal to correct the processing target color signal. What is necessary is just to use for a process. For example, when the processing target color signal is (C, M, Y, K) = (25, 50, 0, 0), the correction is performed to correct C (M, Y, K) = (50, 0). , 0) to select a correction function and correct C. For M, Y, and K, a correction function may be selected from values obtained by fixing the values of other color components, and each correction process may be performed.

  Further, the respective correction functions are not limited to the X component of the colorimetric value, but are obtained for the Y component and the Z component, and before each component of the colorimetric value is predicted, the correction function corresponding to that component is used. It is preferable to correct the processing target color signal.

  Heretofore, some examples of the correction function have been shown. Of course, it goes without saying that the correction function is not limited to these examples. After the correction process using the correction function is performed by the color signal correction unit 11 as described above, the output color signal prediction unit 12 uses a theoretical color prediction model such as the Neugebauer equation or the above-described Neugebauer equation modified by Yule Nielsen. The color (output color signal) that will be output when the processing target color signal is given to the output device is predicted.

  FIG. 12 is an explanatory diagram of an example of prediction of an output color signal. In FIG. 12, colors of C = 25 and M = 50 are given as processing target color signals, and the color signal correction unit 11 performs correction processing using the correction function described in the third example of the correction function described above. It is assumed that the color of C = 50 and M = 75 is obtained as the correction color signal, and the output color signal is predicted. The X component of the colorimetric value corresponding to the reference color of C = M = 0 is Xw, the X component of the colorimetric value corresponding to the reference color of C = 100, M = 0 is Xc, and C = 0, M = 100. The X component of the colorimetric value corresponding to the reference color is Xm, and the X component of the colorimetric value corresponding to the reference color of C = M = 100 is Xb. Xb is assumed to be the X component of the colorimetric value obtained with the color C = M = 50 according to the example shown in FIG.

The weight for each X component obtained from the area ratio is 1/8 for Xw, 1/8 for Xc, 3/8 for Xm, and 3/8 for Xb. When the value of 0 or more and 100 or less is converted into a value of 0 or more and 1 or less in the above equation (1) and n = 1, the X component value Xo of the predicted value is
Xo = Xw / 8 + Xc / 8 + 3.Xm / 8 + 3.Xb / 8
Is calculated by

  If correction processing using the correction function is not performed, the weight for Xw is 3/8, the weight for Xc is 1/8, the weight for Xm is 3/8, and the weight for Xb is 1/8, which is affected by Xb. The influence of Xb in the supposed color is less than that of other X components, which becomes a prediction error. The above value obtained using the correction color signal is the X component of the colorimetric value where Xb is C = M = 50, and the value of C when C = 25 of the color signal to be processed is fixed to M = 50. It corresponds to a position that is 1/2 of the range of 0 to 50 that is the range, and the range of 0 to 75 that is the range of M when M = 50 of the color signal to be processed is fixed to C = 25 It is a value reflecting that it corresponds to the position of 2/3.

  In the above description, the Neugebauer model is used as a theoretical color prediction model. However, a cellular Neugebauer model may be used. For example, when the color signal to be processed is a color signal in the CMYK color space and each color component takes a value of 0 to 100, each color component is divided into 2 to an area of 0 to 50 and an area of 50 to 100. By dividing, the CMYK color space is divided into 16 partial spaces (cells). A correction function is calculated for each of the 16 subspaces, the processing target color signal is corrected using the correction function calculated in the partial space including the processing target color signal, and the noise is corrected in the subspace. A Bauer model may be applied to predict the output color signal. When the cellular Neugebauer model is used, correction processing need not be performed for a partial space that is not subjected to the total amount restriction. In addition, a correction function is not necessary because the entire subspace is outside the total amount limit value because it is not used for prediction. Therefore, the above-described calculation of the correction function and the correction process using the correction function may be performed on the partial space including the total amount restriction boundary.

  In the above description, the CMYK color space is used as the color space of the processing target color signal as an example, or the CM color space is used for simplification of explanation, but of course the color space of the processing target color signal is not limited to these examples. Alternatively, various color spaces having two, three, five or more colors as color components may be used. Further, the color space of the colorimetric values, such as the colorimetric value for the reference color and the colorimetric value in the third example of the correction function described above, is not limited to the above-described example, and uses other spectral reflectances. It may be a color space. What is necessary is just to perform the above-mentioned process according to each color space.

  FIG. 13 is a block diagram showing a second embodiment of the present invention. In the figure, reference numeral 13 denotes a total amount limit value setting unit. In the second embodiment, a total amount limit value setting unit 13 is added to the configuration of the first embodiment shown in FIG. Differences from the first embodiment will be mainly described.

  The total amount limit value setting unit 13 presets a total amount limit value determined from the constraint conditions of the output device.

  The color signal correction unit 11 in the second embodiment corrects the processing target color signal using a correction function when the sum of the color components of the processing target color signal satisfies the total amount limit value, and performs processing When the sum of the color components of the target color signal exceeds the total amount limit value, the correction is performed by a method different from the correction by the correction function. As a method different from the correction by the correction function, for example, it may be corrected to a predetermined value, correction to be converted into the color gamut outline, or other methods may be used.

  Focusing on the third example of the correction function described with reference to FIG. 10 in the first embodiment, the total amount restriction shown in FIG. 10B is imposed, and M = 0 is fixed. In this case, the correction function when M = 100 is fixed does not change so much. For example, the correction function may be represented by a correction function when M is fixed while M = 0. Also, looking at the correction function when the value of C is changed with M = 50 fixed, the correction function in the region exceeding the total amount limit value tends to be linear with respect to the input value, and is determined in advance without correction. Even if the value, for example, 100 is set, the prediction accuracy does not change so much. This is because when the total amount is limited, if the sum of the color components of the color signal used when obtaining the correction function exceeds the total amount limit value, the color signal is changed so that the sum becomes the total amount limit value. This is because the colorimetric values tend to be saturated. In the second example of the correction function described with reference to FIG. 5 in the first embodiment described above, the value of the C component of the processing target color signal is uniformly set to 100 in the region exceeding the total amount limit value. It has been corrected.

  The second embodiment pays attention to this tendency. In the color signal correction unit 11, the sum of the values of the respective color components of the given processing target color signal and the total amount limit value setting unit 13 are set. The total amount limit values are compared, and if the total is within the total amount limit value, correction is performed using a correction function. If the total exceeds the total amount limit value, correction is performed using another method without using the correction function.

  In this configuration, for example, even when the correction function is calculated using the colorimetric values described in the third example of the correction function, the correction function is calculated using the color signal within the total amount limit value and the measurement corresponding to the color signal. There may be a color value, and the correction function may be approximated by a linear function, for example. Alternatively, even when Expression (2) is used, it is only necessary to have a colorimetric value corresponding to the color signal using the maximum value of the color component together with the color signal within the total amount limit value and the colorimetric value corresponding to the color signal. Even when the color signal using the maximum value of the color component exceeds the total amount limit value, the color signal is simply calculated within the total amount limit value for the color signal outside the total amount limit value. A correction function can be obtained with a smaller colorimetric value than in the third example of the correction function described in the first embodiment. Also, a correction function that is not affected by colors outside the total amount limit value can be obtained.

  In the above description, the color signal correction unit 11 determines whether or not to correct the color signal to be processed using the total amount limit value as a determination reference value. However, the present invention is not limited to this, and the total amount limit value + α or the total amount limit value −α is determined. It may be a reference value. The value of α may be determined in advance.

  FIG. 14 and FIG. 15 are explanatory diagrams of an example of a conversion method when the total amount limit value is exceeded in the second embodiment of the present invention. As described above, when the sum of the color components of the color signal to be processed exceeds the total amount limit value, the correction is performed by a method different from the correction by the correction function. As a method different from the correction by the correction function, for example, there is a method of correcting to a predetermined value. An example of this case is shown in FIG. In this example, the predetermined value is C = M = 100, which is a reference color that does not satisfy the total amount limit value, and the processing target color signal exceeding the total amount limit value is uniformly converted to this color. ing. For example, even when the third example of the correction function in the first embodiment described above is used for the processing target color signal that satisfies the total amount limit value, the second example of the correction function is used for the processing target color signal that exceeds the total amount limit value. Correction processing according to the above is performed.

  As another method, a color exceeding the total amount limit value may be corrected to be converted into a color gamut outline when no total amount limit is imposed. An example of this case is shown in FIG. In this example, conversion may be performed so that any one of the color components is 100 while the ratio of the color components outside the total amount limit is left as it is. For example, in the example shown in FIG. 14B, conversion is performed so that one of C and M becomes 100 while the ratio of C and M is left as it is. Specifically, if the color is C = 50 and M = 75, the ratio of C: M = 2: 3 may be left as it is, and C = 67 and M = 100. In this example, when the output color signal prediction unit 12 performs prediction, two-point interpolation of C = 0, M = 100 colorimetric values and C = 50, M = 50 colorimetric values, or Predicted values are calculated for colors exceeding the total amount limit value by interpolation at two points of the colorimetric values of C = 100 and M = 0 and the colorimetric values of C = 50 and M = 50. Therefore, gradation is reproduced even for colors exceeding the total amount limit value.

  As another method, when the third example of the correction function in the first embodiment described above is used for the color signal to be processed that satisfies the total amount limit value, the continuity inside and outside the total amount limit value is considered. Shows how. In FIG. 15A, for example, using the correction function obtained as shown in FIG. 10B, the color before correction when the color signal to be processed is the total amount limit value is a black circle, and after correction. The color is indicated by a white circle. This correction direction is used for colors that exceed the total amount limit value, and conversion is performed while maintaining the correction direction so that either C or M is 100. FIG. 15B shows some colors that exceed the total amount limit value as black circles before correction and white circles after correction.

  Specifically, assuming that the color (C, M) = (25, 75) serving as the total amount limit value is corrected to (C, M) = (73, 97) by the correction function, from (25, 75) Colors that do not satisfy the total amount limit value in the direction toward (73, 97), for example, (C, M) = (49, 86) are corrected so that C or M becomes 100 while maintaining this direction. Thus, (C, M) is corrected to (80, 100).

  In this way, correction processing is performed for colors that do not satisfy the total amount limitation by using the correction direction with the total amount limitation value. Therefore, the continuity of the correction color signal within and outside the total amount limit value is ensured. Note that the output color signal prediction process in the output color signal prediction unit 12 after the correction process is as described in the first embodiment.

  FIG. 16 is an explanatory diagram of an example of a computer program, a storage medium storing the computer program, and a computer when the functions described in the embodiments of the present invention are realized by the computer program. In the figure, 41 is a program, 42 is a computer, 51 is a magneto-optical disk, 52 is an optical disk, 53 is a magnetic disk, 54 is a memory, 61 is a CPU, 62 is an internal memory, 63 is a reading unit, 64 is a hard disk, and 65 is An interface 66 is a communication unit.

  You may implement | achieve the function of each part demonstrated by each embodiment of the above-mentioned all or part by the program 41 which a computer performs. In that case, the program 41 and the data used by the program may be stored in a storage medium read by the computer. The storage medium causes a change state of energy such as magnetism, light, electricity, etc. to the reading unit 63 provided in the hardware resource of the computer according to the description content of the program, and the signal corresponding thereto In this format, the description content of the program is transmitted to the reading unit 63. For example, there are a magneto-optical disk 51, an optical disk 52 (including a CD and a DVD), a magnetic disk 53, a memory 54 (including an IC card, a memory card, a flash memory, and the like). Of course, these storage media are not limited to portable types.

  The program 41 is stored in these storage media, and the program 41 is read from the computer by, for example, mounting these storage media on the reading unit 63 or the interface 65 of the computer 42, and the internal memory 62 or the hard disk 64 (magnetic disk) And the program 41 is executed by the CPU 61, the functions described as the above-described embodiments of the present invention are realized in whole or in part. Alternatively, the program 41 is transferred to the computer 42 via the communication path, and the computer 42 receives the program 41 by the communication unit 66 and stores it in the internal memory 62 or the hard disk 64, and the program 41 is executed by the CPU 61. May be.

  In addition, the computer 42 may be connected to various devices via an interface 65. Of course, it may be partially configured by hardware, or all may be configured by hardware. Or you may comprise as a program which included all or one part of the function demonstrated by each embodiment of this invention with other structures. For example, you may integrate with the other program which uses a predicted value.

  DESCRIPTION OF SYMBOLS 11 ... Color signal correction | amendment part, 12 ... Output color signal prediction part, 13 ... Total amount limitation value setting part, 21 ... Total amount limitation value setting part, 22 ... Total amount limitation part, 23 ... Output device, 24 ... Color measurement part, 31 ... Correction function calculation unit, 41 ... program, 42 ... computer, 51 ... magneto-optical disk, 52 ... optical disk, 53 ... magnetic disk, 54 ... memory, 61 ... CPU, 62 ... internal memory, 63 ... reading unit, 64 ... hard disk, 65: Interface, 66: Communication unit.

Claims (5)

  Among the reference colors used in the theoretical color prediction model, for a reference color that does not satisfy the total amount limit value that is the upper limit of the sum of the values of the color components, a color that satisfies the total amount limit value corresponding to the reference color is defined as the reference color. Alternatively, a correction unit that corrects a processing target color signal given by a correction function that performs correction toward the reference color to obtain a correction color signal, and the total amount limit value of the pair of the reference color and the colorimetric value For a reference color that does not satisfy, a predicting unit that predicts an output color signal from the corrected color signal by a theoretical color prediction model using a colorimetric value obtained in a color that satisfies the corresponding total amount limit value as a pair. A color conversion device characterized by that.   For each color component, the correction means is a plurality of colors in which a certain color component is changed and another color component is fixed, and among the colors that do not satisfy the total amount limit value, the total amount limit value 2. The color according to claim 1, wherein a colorimetric value is obtained for a color changed in a color space so as to satisfy the condition, and correction is performed using a one-dimensional correction function obtained from the change in the colorimetric value. Conversion device.   The correction means obtains the correction function corresponding to each value with other color components fixed for each color component, selects the correction function according to the value of the fixed color component, and selects the corresponding color The color conversion apparatus according to claim 2, wherein the component is corrected.   The correction means performs correction by the correction function when the total sum of color components of the processing target color signal satisfies the total amount limit value, and the total sum of color components of the processing target color signal sets the total amount limit value. 4. The color conversion apparatus according to claim 1, wherein if it exceeds, correction is performed by a method different from correction by the correction function. 5.   A color conversion processing program for causing a computer to execute the function of the color conversion apparatus according to any one of claims 1 to 4.

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