JP2007043250A - Color conversion method, color conversion apparatus, color conversion program, and storage medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a color conversion apparatus and a color conversion method whereby an output device reproduces colors of a target device with high accuracy and high gradation by keeping a ink version in the target device as much as possible within a range of placing a limit on a color material total amount of the output device and ensuring the monotonousity of color materials other than the ink. <P>SOLUTION: An optimum ink amount determining section 13 in the color conversion apparatus determines an optimum ink amount on the basis of a ink amount K and device independent color signals resulting from converting CMYK color signals of the target device. In this case, the color conversion apparatus calculates a proper total amount limit value by each ink amount so as to make the upper limit of the total amount of the color materials except the ink color constant, generates lower side outer shell face device independent color signals for configuring a lower side outer shell face corresponding to each ink amount on the basis of the proper total amount limit value by each ink amount, and generates a model for calculating the proper ink amount corresponding to each device independent color signal on the basis thereof. The color conversion apparatus uses this model to calculate the proper ink amount on the basis of the device independent color signals of the target device and calculates the ink amount of the output device color signal on the basis of each of the proper ink amount and the ink amount of the target device color signals. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a color to be converted from a target device color signal in a target device in an N (N ≧ 4) dimensional color space including black to an output device color signal in an output device in an M (M ≧ 4) dimensional color space including black. It relates to conversion technology. More specifically, for the purpose of simulating the color output by the target device with the output device, the total color material amount limit is set for the color output by the target device while retaining the black version of the target device as much as possible. The present invention relates to a color conversion technique for reproducing with high accuracy and good gradation with an imposed output device.

  There is a technique for simulating color reproduction of different color output devices (target devices) with color output devices including black, such as CMYK. This technique is called ink simulation, and is used for applications such as simulating color reproduction of a printing press with a printer to realize proofing at low cost. In addition, since the K (black) plate of the printing image is held as much as possible on the printer side, the color reproduction texture and sharpness can be held, so a technique called K plate holding is also an essential technique for ink simulation. Yes.

  However, since the color reproduction characteristics of the target device and the output device are generally different, if you try to simulate the color reproduction on the target device by using the black plate on the target device as it is on the output device, it can be reproduced on the output device. The effective color reproduction range cannot be used effectively. In addition, xerographic printers and inkjet printers used for simulation often have a limit on the total amount of color material that can be used, and this total color material amount limit is the difference in color reproduction characteristics from the target device. To make it bigger.

  Thus, in order to realize a highly accurate ink simulation while keeping the black plate of the target device as much as possible, a technique for determining an appropriate black amount in the output device is indispensable.

  As one of such techniques, there is a method described in Patent Document 1. The method described in Patent Document 1 uses a color signal in a device-dependent color space (hereinafter referred to as a target device color signal) of a target device to be processed as a color signal in a device-independent color space (hereinafter referred to as a device independent color). Signal), the minimum black amount that satisfies the total color material amount limit that can be reproduced by the output device from the device independent color signal is calculated. Then, an appropriate black amount is determined according to the saturation from the minimum required black amount and the black amount of the target device color signal. Further, the output device color signal is calculated from the device independent color signal to be processed and the calculated appropriate black amount.

  The method described in Patent Document 1 has a problem that it takes a long processing time because the minimum black ink amount is calculated by searching in a device-independent color space. As a countermeasure for such a problem, for example, there is a method described in Patent Document 2. In this method, instead of exploringly calculating the minimum required black amount that satisfies the total amount of color material that can be reproduced by the output device, the device independent color signal as a target in Patent Document 1, Build a model that calculates the minimum required black amount from any device-independent color signal by calculating the required black amount pair, and calculate the minimum required black amount at high speed by using this model It is a method to do.

  Here, the pair of the device independent color signal and the minimum required black amount is a device corresponding to an output device color signal in which any color material except black is 100% or equal to the total color material amount limit value. It can be created by the independent color signal and the corresponding black amount.

  FIG. 9 shows that in the device independent color space, any one of the color materials excluding black is 100%, or the black color composed of the device independent color signal corresponding to the output device color signal equal to the total color material amount limit value. It is explanatory drawing of an example of a change when changing the amount of black of the lower outer surface for every quantity. The black circle in the figure is a device independent color signal, and the black amount associated with the lower outer surface on which the black circle is placed is the minimum necessary black amount corresponding to the device independent color signal.

  According to the conventional technology as described above, it is possible to simulate the color reproduction of the target device with high accuracy while keeping the black plate of the target device as much as possible while effectively using the color gamut of the output device.

  However, in the conventional technique described above, since the black plate of the target device is held as much as possible, there may be a problem in the continuity of color signal components other than black.

  FIG. 10 is an explanatory diagram of an example of the color gamut outline and the lower outline of the CMYK output device in which 240% is uniformly imposed as the total color material amount limit value in the device independent color space. In FIG. 10, the color gamut outline when the black amount is 0% and the lower outer surface when the black amount is 21%, 42%, 60%, 81%, and 100% are indicated by solid lines. Further, a curve in the vicinity of the achromatic color axis assuming a device independent color signal corresponding to the process black gradation in the target device is represented by a broken line. The black circle on the broken line is the intersection with the lower outer surface for each black amount.

  In the conventional technology, in order to keep the black plate of the target device as much as possible, the black amount of the color signal of the CMYK output device that reproduces the device independent color signal indicated by the black circle corresponds to the solid line on which the black circle is placed. The amount of black will be used. Therefore, the color signals of the CMYK output device that reproduces the black circles are, for example, (C, M, Y, K) = (80, 80, 80, 0), (73, 73, 73, 21), in order from the brightest. (66, 66, 66, 42), (60, 60, 60, 60), (53, 53, 53, 81), (46, 47, 47, 100). Strictly speaking, the gray level of the process black of the target device and the gray level of the process black of the output device do not match. However, for convenience of explanation, the C, M, Y is assumed to be approximately equal.

  FIG. 11 is a graph showing an example of the relationship between the process black gradation of the target device and the coverage of each color component in the output device in the prior art. As shown in FIG. 10, in the CMYK output device color signal that reproduces the process black gradation in the target device, C, M, and Y increase monotonously within a range that can be reproduced while maintaining the black amount. If the color cannot be reproduced while maintaining the black amount, the black amount increases monotonously and C, M, and Y decrease simultaneously to secure the minimum required black amount. FIG. 11 is a graph showing this situation.

  In FIG. 11, the horizontal axis represents the CMY coverage as the process black (gray) gradation of the target device, and the vertical axis represents the CMY and K coverage of the color signals of the CMYK output device holding the black plate as much as possible. . 0% on the horizontal axis indicates white color with C = M = Y = 0%, and 100% indicates process black with C = M = Y = 100%. Here, since it is assumed that the total color material amount limit value is 240%, it is possible to reproduce up to C = M = Y = 80% of the output device by the process black by CMY. Even if the black plate is not used, the output device needs to reduce the CMY by adding black so as to satisfy the total color material amount limit value. In this example, the CMYK output device color signal has a peak when the target device process gray (C, M, Y, K) = (50, 50, 50, 0).

  As described above, when the color signal of the CMYK output device for reproducing the monotonous gradation in the target device has a peak, an error becomes large during actual color conversion, and good color reproduction cannot be performed. is there. For example, when a multi-dimensional lookup table (multi-dimensional LUT) is used for color conversion, the grid points storing values in the table do not always coincide with the peaks shown in FIG. Therefore, even if the output value of each grid point in the multi-dimensional LUT can be calculated with high accuracy, the color between the grid points is obtained by interpolation from the surrounding grid points. There is a problem that the reproduction accuracy is lowered and a defect such as a gradation jump is caused.

JP 2002-112269 A JP 2005-64774 A

  The present invention has been made in view of the above-described circumstances, and retains the black plate in the target device as much as possible within a range satisfying the restriction on the total amount of color material imposed on the output device, and color materials other than black An object of the present invention is to provide a color conversion device and a color conversion method that can reproduce the color output from the target device with high accuracy and good gradation with an output device in which the limitation on the total amount of color material is imposed. To do. It is another object of the present invention to provide a color conversion program for realizing such a color conversion method by a computer and a storage medium storing such a color conversion program.

  In the present invention, the total amount limit value is changed so that the upper limit value of the total amount of the color material excluding black does not have a peak as shown in FIG. The appropriate total amount limit value is calculated for each amount. For example, the upper limit value of the total amount of color materials excluding black can be made constant as a value obtained by subtracting 100% from the limit value of the total amount of color material imposed on the output device, and the appropriate total amount limit value can be calculated. Based on the appropriate total amount limit value, a lower outer surface device color signal constituting the lower outer surface in the device color space of the output device corresponding to each black amount is obtained, and the lower outer surface device color signal is obtained. A model for calculating a device-independent color signal corresponding to the device-independent color signal from the device-independent color signal and the black amount of the lower outer surface to which the device-independent signal belongs. A proper black amount is calculated from the device independent color signal using the created model, and the black amount of the output device color signal is calculated from the proper black amount and the black amount of the target device color signal.

  In the present invention, the total amount limit value is changed so that the upper limit value of the total amount of the color material excluding black is constant on the achromatic color reference line set near the achromatic color axis in the device-independent color space as described above. Calculate the appropriate total amount limit value for each black amount, and use the appropriate total amount limit value for each black amount on the achromatic color reference line as a reference, and the total amount limit value as you approach the outline of the color gamut limited to the corresponding black amount The appropriate total amount limit value for each black amount other than the achromatic color reference line is determined so that increases monotonously. A lower outer surface device color signal constituting the lower outer surface in the device color space of the output device corresponding to the black amount is obtained from the appropriate total amount limit value determined for each black amount, and the lower outer surface device color signal is obtained. The corresponding device independent color signal is calculated from the surface device color signal, and the appropriate black amount corresponding to the device independent color signal is calculated from the device independent color signal and the black amount of the lower outer surface to which the device independent signal belongs. Create a model, calculate the appropriate black amount from the device independent color signal using the created model, and calculate the black amount of the output device color signal from the appropriate black amount and the black amount of the target device color signal .

  Furthermore, in the present invention, a model as described above is created for each black amount in the target device, and a model corresponding to the black amount of the target device color signal is selected and used to calculate the appropriate black amount. The black amount of the output device color signal can be calculated from the black amount of the device color signal. In this case, the black amount of the output device that is the minimum necessary to reproduce the color gamut in the device-independent color space of the target device color signal when the black amount of the target device is fixed and the black amount of the target device is set. Obtain the minimum black amount that is the amount, determine the upper limit of the total amount of color material excluding black at that minimum black amount, and set the appropriate total amount limit value for each black amount of the output device so that the upper limit value is constant Is calculated. This upper limit value can be larger than when the black amount of the target device is not fixed, and the range of values that each color material can take is widened so that the black of the target device can be maintained more. Can do. Then, from the appropriate total amount limit value for each black amount of the output device, a lower outer surface device independent color signal constituting the lower outer surface in the device independent color space corresponding to the black amount can be created, and a model can be created. it can.

  When calculating the appropriate total amount limit value for each black amount, it increases monotonically from the upper limit of the total amount of color material excluding black, which should be kept constant, as the black amount decreases to 0% when the black amount is 100%. However, it is possible to calculate a proper total amount limit value for each black amount by subtracting a predetermined margin that becomes a maximum value when the black amount is 0%. Thereby, for example, when the process device gradation of the target device is reproduced by the output device, the amount of change in the color signal other than black before and after the start of black can be reduced.

  According to the present invention, the ink is determined by dynamically determining the appropriate total amount limit value according to the target color signal in the device independent color space based on the uniform total color material amount limit set in the output device. Since it eliminates the peak of the color material amount excluding the color and ensures monotonicity, it satisfies the limitations on the total color material amount of the output device and retains the black plate on the target device as much as possible, while interpolating errors due to the multidimensional LUT. The amount of color material other than black can be determined with high accuracy. As a result, there is an effect that the color output by the target device can be reproduced with high accuracy and good gradation by the output device on which the restriction on the total amount of the color material is imposed.

  FIG. 1 is a block diagram showing a first embodiment of the present invention. In the figure, 11 is a target device forward conversion unit, 12 is a color gamut mapping unit, 13 is an optimum black amount determination unit, and 14 is an output device reverse conversion unit. In the following description, the target device is a CMYK printer, the output device is a CMYK printer, and the target device color signal (CMYK) is converted into an output device color signal (C′M′Y′K ′). explain. Further, it is assumed that the target device color signal is converted into the output device color signal while keeping the black value (hereinafter, black amount) of the target device color signal as much as possible. Note that the CIELAB color space is used here as the device-independent color space used during the processing.

  The target device forward conversion unit 11 converts the target device color signal (CMYK) to be converted into a CIELAB color signal (LAB) that is a device independent color signal according to the color reproduction characteristics of the target device. This conversion method can be implemented by using a model based on matrix conversion, a neural network, or the like. Further, for example, a regression model described in JP-A-10-262157 can be used.

  The color gamut mapping unit 12 maps the CIELAB color signal (LAB) converted by the target device forward conversion unit 11 to a CIELAB color signal (L'A'B ') in a color range (Color Gamut) that can be reproduced by the output device. . As the mapping method, various known methods can be used.

  The optimum black amount determination unit 13 determines the appropriate black amount (K of the output device color signal) from the CIELAB color signal (L′ A′B ′) output from the color gamut mapping unit 12 and the black amount of the target device color signal. ') Is calculated. Details of the optimum black amount determination unit 13 will be described later.

  The output device inverse conversion unit 14 uses the black amount (K ′) and the CIELAB color signal (L′ A′B ′) in the output device to output an output device color signal (C ′) that excludes black according to the color reproduction characteristics of the output device. M′Y ′) is calculated.

  With such a configuration, the target device color signal (CMYK) can be converted into the output device color signal (C′M′Y′K ′) while maintaining the black amount of the target device color signal as much as possible. For example, the CMYK color signals corresponding to the pixels of the CMYK image may be directly color-converted using the configuration described above, or the CMYK color signals corresponding to the grid points of the multidimensional lookup table may be color-converted, A multi-dimensional lookup table that realizes color conversion may be created, and CMYK image color conversion may be performed using the multi-dimensional lookup table.

  Hereinafter, the optimum black amount determination unit 13 will be described in detail. FIG. 2 is an explanatory diagram of an example of an appropriate black amount limit value and a lower outline surface for each black amount set in the first embodiment of the present invention. Meanings of black circles, solid lines, and broken lines in the figure are the same as those in FIG.

  The cause of the problem in the conventional technology is that the lower outer surface is configured for each black ink amount based on the uniform total color material amount limit value. When the amount of ink increases, the degree of freedom of color materials other than ink decreases. Here, the degree of freedom of the color material means the upper limit of the total amount of color material for the color materials other than black, and naturally the number of combinations of color materials that matches the upper limit of the total amount of color material decreases as the degree of freedom decreases. For this reason, as shown in FIG. 10, C, M, and Y, which can be assumed to be almost gray on the lower outer surface of 0%, are secured at 80%, whereas the amount of ink is 100. C, M, and Y of the point that can be assumed to be almost gray on the lower outer surface of% can be secured only about 46 to 47%, and the color other than black of the output device color signal that reproduces the monotonous gradation of the target device A peak occurs in the component.

  Therefore, in the present invention, when reproducing the monotonous gradation of the target device with an output device in which a uniform total color material amount restriction is imposed, the monotonicity of the color components other than black cannot be secured and has a steep peak. In order to solve the problem in the prior art that a large interpolation error occurs when used as a parameter such as a multidimensional LUT, a method of dynamically controlling the upper limit of the total amount of color material for each black amount Take. That is, when constructing the lower outline for each black amount, instead of using a uniform total color material amount limit value, the overall color material total amount limit value is not exceeded, and at the same time, other than black By making the upper limit of the total color material amount constant, the monotonicity of the total color material amount other than black is ensured.

  For example, in the example shown in FIG. 2, the upper limit of the total amount of color material other than black is set equal to the upper limit of the total amount of color material other than black when the black amount is 100%. An example in which an upper limit value is set and a lower outline for each black amount is configured is shown. In this example, since the restriction on the total amount of color material of the output device is 240%, 140% obtained by subtracting 100% from 240%, which is the restriction on the total amount of color material of the output device, is used as the total amount of color material other than black. The upper limit. If the upper limit of the total amount of color material other than black is 140%, even if black is 100%, the limit of the total color material amount of the output device is not exceeded. The appropriate total amount limit value for each black amount can be obtained by adding the black amount to the upper limit of the total color material amount other than black. Accordingly, the appropriate total amount limit value varies depending on the black amount. When the black amount is 0%, the upper limit of the total color material amount other than black is 140%, and when the black amount is 100%, the total color material amount of the output device. The limit is 240%.

  As can be seen from FIG. 2, the upper limit of the total amount of C, M, and Y is made constant at 140%, and the lower outer surface of each black amount is configured to output the process black gradation of the target device as CMYK. It can be seen that each color component of the color signal reproduced by the device does not decrease at least as the amount of black increases, and thus the peak that caused the interpolation error in the conventional technique is eliminated.

  FIG. 3 is a graph showing an example of the relationship between the process black gradation of the target device and the coverage of each color component in the output device according to the first embodiment of the present invention. If the gradation of the process black of the target device, the black amount shown in FIG. 2 and the coverage of the color material other than black are graphed similarly to FIG. 11, the result is as shown in FIG. As can be seen from a comparison with FIG. 11, there is no peak in the coverage of the color material other than black, and for example, the occurrence of errors can be suppressed even when interpolation is used.

  FIG. 4 is a block diagram illustrating an example of the optimum black amount determination unit. In the figure, 21 is a proper virtual surface device color signal group creation unit, 22 is a proper black amount calculation model creation unit, 23 is a proper black amount calculation unit, and 24 is an optimal black amount calculation unit. With the configuration shown in FIG. 1, the optimum black amount determination unit 13 converts the target device color signal (CMYK) into the CIELAB color signal (LAB) and performs the color gamut mapping process. It is assumed that the black amount of the target device color signal is given as (L′ A′B ′) (hereinafter referred to as device independent color signal).

The appropriate virtual surface device color signal group creation unit 21 first sets the upper limit value of the total amount of color material excluding black for each black amount (K) in the output device on which the uniform total color material amount limit is imposed. Thus, an appropriate total amount limit value (TC) is calculated. The appropriate color material total amount limit value TC is, for example, TC (K) = R− (100−K).
It can ask for. Here, R is a limit value of the uniform total amount of color material imposed on the output device.

  Furthermore, the appropriate virtual surface device color signal group creation unit 21 satisfies the appropriate total amount limit value for each calculated black amount, and the device of the output device that constitutes the lower outline in the device-independent color space corresponding to each black amount Create a color signal group. Here, the lower outer surface of each black amount that satisfies the appropriate color material total amount limit value is configured by CMYK color signals in which either C, M, or Y is 100% or equal to the appropriate color material total amount limit value. Therefore, for example, C, M, and Y that can be created within the CMY total amount value obtained by subtracting the corresponding black amount from the appropriate color material total amount limit value corresponding to the black amount by shaking the black amount set in increments of 10%. Should be created. The step size and the like are arbitrary. Of course, C, M, and Y that can be created may be calculated using the fact that this CMY total amount value becomes (R-100) regardless of the black amount. The device color signal group constituting the lower outer surface calculated here is passed to the appropriate black amount calculation model creation unit 2.

  The appropriate black amount calculation model creation unit 22 converts the device color signal group of the output device constituting the lower outline created by the proper virtual surface device color signal group creation unit 21 into a device independent device that is a color signal of a device independent color space. A color signal is converted, and a model for calculating the optimum black amount corresponding to the device-independent color signal is created from the device-independent color signal and the black amount (K) of the device color signal corresponding to the device-independent color signal. For example, using the method described in Patent Document 2, a model can be created for the device color signal group created by the appropriate virtual plane device color signal group creation unit 21. The present invention is not limited to these methods, and any method that can calculate an appropriate black amount by giving an arbitrary device independent color signal from discretely distributed device independent color signals and the corresponding appropriate black amount. Any method may be used.

  The appropriate black amount calculation unit 23 calculates the appropriate black amount created by the appropriate black amount calculation model creation unit 22 from the device independent color signal (CIELAB color signal) to be converted into the device color signal of the CMYK printer as the output device. The appropriate black amount is calculated using the model.

  The optimum black amount calculation unit 24 controls the degree of black plate retention according to the saturation, for example, from the appropriate black amount calculated by the appropriate black amount calculation unit 23 and the black amount of the target device color signal, and outputs the device color signal. The amount of black is calculated. For example, a technique described in Japanese Patent Application Laid-Open No. 2004-112269 can be applied to the optimum black amount calculation unit 24. In the present invention, the optimum black amount calculation unit 24 may be omitted. In this case, the appropriate black amount calculated by the appropriate black amount calculation unit 23 may be output as the optimal black amount.

  As described above, in the present invention, in the device-independent color space, the black including the black with the uniform limitation on the total color material amount is imposed so that the upper limit value of the total color material amount other than black is constant regardless of the black amount. The appropriate black amount is calculated by determining the appropriate total color material amount limit value for each black amount of the color output device of dimension or higher. Thus, the device color signal for reproducing the target device color signal by the color output device can be uniquely determined with continuous and monotonicity. Therefore, for example, even when color conversion is performed by calculating a color conversion parameter for reproducing a target device color signal with a color output device as a multi-dimensional LUT, it is possible to reduce the occurrence of interpolation error. The occurrence of key jumps can be suppressed.

  Next, a second embodiment of the present invention will be described. The configuration of the second embodiment is the same as the configuration of the first embodiment shown in FIGS. 1 and 4, and different parts will be described below.

  In the first embodiment described above, the appropriate total amount limit value for each black amount is uniformly applied to each black amount. For this reason, for example, when the uniform total color material amount limit imposed on the output device is less than 300%, the appropriate total color material amount limit value for each black amount is less than 200% depending on the black amount, and does not include black. The solid color (total color material amount is 200%) exceeds the appropriate total color material amount limit value and cannot be output. Therefore, although good color reproduction can be realized while suppressing the occurrence of gradation jumps, it also has the disadvantage that the color reproduction range of the output device becomes narrow.

  In the second embodiment, the appropriate color material total amount limit value on the lower outer surface for each black amount is R- (100-K) in the vicinity of the achromatic color axis, and from the achromatic color axis on the lower outer surface. An example is shown in which the appropriate color material total amount limit value on the device independent color space is determined so that the appropriate color material total amount limit value increases monotonously with increasing distance.

  FIG. 5 is an explanatory diagram of an example of a lower outer surface for each black amount created in the second embodiment of the present invention. The meanings of black circles, solid lines, broken lines, etc. in the figure are the same as those in FIGS. FIG. 5 shows an example of a case where the lower outline is configured by changing the appropriate color material total amount limit value in the vicinity of the achromatic color axis (broken line in the drawing) and the vicinity thereof. In the example shown in FIG. 5, the appropriate total color material amount limit value is set to R- (100-K) in the vicinity of the achromatic color axis, and the uniform total color material amount limit value imposed on the output device on the lower outer surface. The appropriate total amount limit value at the boundary portion where output is possible (only a part is indicated by a black square in FIG. 5) is R (a uniform limit value for the total amount of color material imposed on the output device). Is determined as the appropriate total color material amount limit value so as to change monotonously.

In the second embodiment, in order to set the appropriate color material total amount limit value as described above, the process of the appropriate virtual surface device color signal group creation unit 21 may be changed in the configuration shown in FIG. The appropriate virtual surface device color signal group creation unit 21 in the second embodiment calculates an appropriate color material total amount limit value TC for each black amount K in the output device to which the uniform color material total amount limit R is imposed.
TC (C, M, Y, K) = R− (100−K) (1−Ch (C, M, Y)) ^γ
And a lower outer surface device independent color signal constituting the lower outer surface for each black amount satisfying this appropriate color material total amount limit value is created. Here, Ch (C, M, Y) is a saturation that can be determined from the color signals C, M, and Y of the output device corresponding to the color signal in the device-independent color space for which the appropriate total color material amount limit value is calculated. In this case, Ch (C, M, Y) = 0 when C = M = Y, and 1 when C or M or Y is 0% or 100%. Γ is a gamma coefficient for designating how to change the appropriate total color material amount limit value from R to R- (100-K) with respect to the change of the saturation index, and can be arbitrarily set. is there.

  As a method for creating the lower outer surface device independent color signal constituting such lower outer surface, here, the total color material amount limit value in the output device once imposed a uniform total color material amount limitation. The CMYK color signal group on the lower outer surface for each black amount satisfying R is calculated, and the CMYK color signal satisfying the appropriate color material total amount limit value described above is corrected for each of the calculated CMYK color signals. The lower outer surface device independent color signal is created.

  First, the lower outer surface of each black amount satisfying the uniform color material total amount limit value R is determined from the CMYK color signal in which either C, M, or Y is 100% or equal to the color material total amount limit value R. Therefore, for example, the black amount set in a predetermined step such as 10% is shaken, and the above-described CMY total amount value obtained by subtracting the corresponding black amount from the total color material amount limit value R corresponding to the black amount is described above. C, M, and Y satisfying the above condition are created.

Next, for the CMYK color signal equal to the uniform color material total amount limit value R among the generated CMYK color signals, the above-described TC (C, M, Y, K) = R− (100−K) (1− Ch (C, M, Y)) ^γ is calculated to calculate an appropriate color material total amount limit value, and the original CMYK color signal is corrected so as to be equal to the appropriate color material total amount limit value. For example, the ratio of the original C, M, Y color components is stored, and the CMYK color signal is corrected so that the sum of C, M, Y, K is equal to the appropriate color material total amount limit value without changing K. be able to. Also, the sum of C, M, Y, and K is not the ratio of the C, M, and Y color components, but the sum of C, M, Y, and K is the proper color by subtracting an equal amount from the color components having positive values among the original C, M, and Y color components. The CMYK color signal can also be corrected so as to be equal to the total material amount limit value.

  By configuring the appropriate virtual surface device color signal group generation unit 21 to perform such processing, the appropriate black amount calculation model generation unit 22, the appropriate black amount calculation unit 23, and the optimum black amount calculation unit 24 are not changed. Can be applied as it is.

  When determining the lower outer surface for each black amount that satisfies the uniform color material total amount limit value R, it is preferable that the lightness does not reverse as the black amount increases. For example, a total amount limit value smaller than a uniform color material total amount limit value R is set for each black amount as necessary so that the brightness decreases as black increases at the points indicated by black squares in FIG. The lower outer surface should be constructed. Further, the achromatic color axis reference line indicated by a broken line in FIG. 5 is a color signal group in a device-independent color space corresponding to process black in the target device or the output device, or a lightness axis in a device-independent color space. can do. Of course, it can be arbitrarily set. Further, in the second embodiment, similarly to the first embodiment described above, the process of the optimal black amount calculation unit 24 is omitted and the appropriate black amount is output as the optimal black amount. Also good.

  As described above, according to the second embodiment, in addition to the effects of the first embodiment, the output device in which a uniform total color material amount limit value of 200% or more and less than 300% is imposed. Even in this case, it is possible to output a solid secondary color, and there is an effect that a color gamut that can be originally output by the output device can be used.

  Next, a third embodiment of the present invention will be described. The configuration of the third embodiment is the same as the configuration of the first embodiment or the second embodiment shown in FIGS. 1 and 4, and the differences will be described below. Go.

In the third embodiment, an example in which a margin is provided for the appropriate total color material amount limit value will be described. For example, in the first embodiment described above, the total color material amount excluding black is made constant at R-100, and the appropriate color material total amount limit value is obtained as TC (K) = R− (100−K). In the second embodiment described above, the appropriate color material total amount limit value is TC (C, M, Y, K) = R− (100−K) (1−Ch (C, M, Y)) ^γ. Looking for. However, since the amount of change in the color material other than black that has been increased before and after the color at which the ink starts to enter becomes 0 as it is, the change in the amount of change in the color material other than the ink becomes large. Interpolation error may become slightly larger at this part. In order to prevent such a problem, it is possible to provide a margin for giving a trend of increasing the color material other than black even if the ink starts to enter.

For example, a margin is provided for the appropriate color material total amount limit value in the first embodiment described above,
TC (K) = R− (100−K) −α (1−K / 100) ^β
It can be. In the second embodiment described above, a margin is provided for the appropriate color material total amount limit value,
TC (C, M, Y, K) = R- (100-K) (1-Ch (C, M, Y)). ^Gamma .-. Alpha. (1-K / 100) ^.beta.
It can be. Here, α (1−K / 100) ^β is a margin of the appropriate color material total amount limit value, and when K = 0%, the appropriate color material total amount limit value is lowered by α. Also, β is a gamma coefficient that designates how to change K with respect to K, while a margin of 0 is secured when K = 100% and 0 when K = 0%.

  FIG. 6 is an explanatory diagram showing an example of the margin of the appropriate total color material amount limit value according to the third embodiment of the present invention. In this example, the relationship between the process black gradation of the target device and the coverage of each color component of the output device in the achromatic color reference line of the first embodiment or the second embodiment described above is shown. . In FIG. 6, for example, the coverage of the color material other than black shown in FIG. 3 is indicated by a broken line. In the portion after the ink starts to be added, in the third embodiment, a margin is provided to give a trend of increasing the color materials other than the ink.

  By introducing such a margin, it is possible to reduce the interpolation error even in the color of the portion where the ink begins to enter on the lower outer surface for each ink amount. In addition, since C, M, and Y can be gradually increased as the amount of black increases, color signal components C and M of gradations to be reproduced even for gradations that do not match the achromatic reference line. , Y peak can be reduced. However, since the degree of black plate storage is low, adjustment is made with parameters α and β. Although the margin α can take a negative value, in this case, although there is an effect of increasing the degree of black plate retention, it is easy to generate a peak in the color signal components C, M, and Y of the gradation to be reproduced. Therefore, it is necessary to set an appropriate value according to the purpose.

  Next, a fourth embodiment of the present invention will be described. The configuration of the fourth embodiment is the same as the configuration of the first embodiment shown in FIGS. 1 and 4 or the configuration of the second and third embodiments. I will explain to you.

  In the fourth embodiment, the appropriate virtual surface device color signal group creation unit 21 and the appropriate black amount calculation model are described for each black amount of the target device as described in the first to third embodiments. When the creation unit 22 creates a model and the appropriate black amount calculation unit 23 uses the model, the model corresponding to the black amount of the target device is selected and used to calculate the appropriate black amount and the optimal black amount. At this time, by fixing the black amount of the target device, the color gamut that can be taken is narrowed, and the range of the black amount that is required at the minimum when the output device reproduces the color gamut can be narrowed. Based on the maximum value of the black amount in the narrowed range, the total color material amount other than black can be set constant (or including a margin). As a result, the range that the color material other than black can take can be expanded, and the degree to which the black plate of the target device can be held can be increased.

  FIG. 7 is an explanatory diagram of an example of a lower outer surface for each color reproduction range and black amount of the target device in a certain black amount in the fourth embodiment of the present invention. Meanings of black circles, solid lines, and broken lines in the figure are the same as those in FIG. In FIG. 7, a color gamut in which the black amount of the target device is 0% is indicated by a dotted line. In the example shown in FIG. 7, the minimum black amount on the output device side required to reproduce the color signal with the black amount of the target device being 0% is 60%. That is, the color of the lower outline in which the black amount is 81% or 100% is a color that does not need to be reproduced when the black amount of the target device is 0%. Therefore, for example, it is not necessary to subtract 100 from the uniform color material total amount limit value R as in the first embodiment. In this example, it is only necessary to subtract 60. Therefore, in this example, the appropriate color material total amount limit value TC when the black amount of the target device is 0% may be TC (K) = R− (60−K). For example, when the limit value of the uniform total color material amount is 240%, when 100 is reduced as in the first embodiment, the appropriate color material total amount limit value TC when K = 0% is 140%. However, when 60 is reduced, the appropriate total color material amount limit value TC when K = 0% is 180%, and the reproducible range is widened by K = 0%. In this way, the appropriate total color material amount limit value TC can be increased, and the range in which the black amount can be stored can be expanded.

Here, assuming that the minimum black amount on the output device side for reproducing the color signal when the black amount of the target device is a certain value is KB, the appropriate color material total amount limit value TC is the first implementation. TC (K) = R− (KB−K) in the case of the method of the form
Can be obtained as In the case of the method of the second embodiment,
TC (C, M, Y, K) = R− (KB−K) (1−Ch (C, M, Y)) ^γ
Can be obtained as Further, in the method of the third embodiment, a margin term (−α (1-K / 100) ^β ) may be added.

  According to the configuration of the fourth embodiment, it is possible to improve the degree of black plate retention as described above, but for each black amount in the color signal of the target device, an appropriate virtual surface device color signal group creation unit 21 and the appropriate black amount calculation model creation unit 22 construct a model for calculating the appropriate black amount, and the processing time increases.

  In the color signal of the target device shown in FIG. 7, the range that can be taken by the black amount of the output device color signal that can reproduce the color when fixed to a certain black amount is described in, for example, Japanese Patent Application No. 2005-147597. It can be calculated using a required black amount calculation model based on a required total amount limit value that does not intersect the lower outer surface for each black amount of the output device. That is, the essential total amount limit value for each black amount is calculated so that the lower outer surfaces in the device independent color space for each black amount of the output device color signal do not intersect each other, and the lower limit that satisfies the essential total amount limit value for each black amount is calculated. A device independent color signal group constituting the side outline is calculated, and an essential black amount calculation model is created from a pair of the device independent color signal group and the black amount. Using this essential black amount calculation model, the maximum black amount used for reproducing the color signal when the black amount of the target device is fixed by the output device can be calculated. For example, when the black amount of the target device is 0%, a device independent color signal corresponding to the target device color signal (C, M, Y, K) = (100%, 100%, 100%, 0%) is calculated. Then, the black amount may be obtained from the device independent color signal using the essential black amount calculation model. Thereby, the maximum black amount used for reproducing the color signal with the black amount of the target device being 0% by the output device can be calculated. An appropriate color material total amount limit value that is appropriate for each black amount of the target device can be calculated from the above-described equation with the maximum black amount calculated in this way as KB.

  FIG. 8 is an explanatory diagram of an example of a computer program and a storage medium storing the computer program when the function of the color conversion apparatus or the color conversion method of the present invention is realized by the computer program. In the figure, 31 is a program, 32 is a computer, 41 is a magneto-optical disk, 42 is an optical disk, 43 is a magnetic disk, 44 is a memory, 51 is a magneto-optical disk apparatus, 52 is an optical disk apparatus, and 53 is a magnetic disk apparatus.

  The configuration described as each of the above-described embodiments or part or all of the modifications thereof can be realized by a program 31 that can be executed by a computer. For example, all the steps shown in FIG. 1 and FIG. 4 described above, the step of creating a model for calculating the appropriate black amount shown in FIG. 4, or the model for calculating the appropriate black amount created in advance is used. Thus, the process of performing the color conversion process can be realized by a program. When implemented as a program in this manner, the program 31 and data used by the program can be stored in a computer-readable storage medium. A storage medium is a signal format that causes a state of change in energy such as magnetism, light, electricity, etc. according to the description of a program to a reader provided in the hardware resources of a computer. Thus, the description content of the program can be transmitted to the reading device. For example, there are a magneto-optical disk 41, an optical disk 42 (including a CD and a DVD), a magnetic disk 43, a memory 44 (including an IC card and a memory card), and the like. Of course, these storage media are not limited to portable types.

  By storing the program 31 in these storage media and mounting these storage media in, for example, the magneto-optical disk device 51, the optical disk device 52, the magnetic disk device 53, or a memory slot (not shown) of the computer 32, the computer 31 The program 31 can be read to execute the function of the color conversion apparatus or the color conversion method of the present invention. Alternatively, a storage medium may be mounted or built in the computer 32 in advance, and the program 31 may be transferred to the computer 32 via a network, for example, and the program 31 may be stored in the storage medium and executed. Of course, some functions may be configured by hardware, or all may be configured by hardware.

It is a block diagram which shows the 1st Embodiment of this invention. It is explanatory drawing of an example of the appropriate black amount limit value for every black amount set in the 1st Embodiment of this invention, and a lower outer surface. It is a graph which shows an example of the relationship between the gradation of the process black of the target device in the 1st Embodiment of this invention, and the coverage of each color component in an output device. It is a block diagram showing an example of an optimal black amount determination unit. It is explanatory drawing of an example of the lower outer surface for every black amount created in the 2nd Embodiment of this invention. It is explanatory drawing of an example of the margin of the appropriate color material total amount restriction | limiting value in the 3rd Embodiment of this invention. In the 4th Embodiment of this invention, it is explanatory drawing of an example of the lower outer surface for every color reproduction range and black amount of the target device in a certain black amount. It is explanatory drawing of an example of the storage medium which stored the computer program in the case of implement | achieving the function of the color conversion apparatus or color conversion method of this invention with a computer program, and the computer program. In the device independent color space, either one of the color materials excluding black is 100%, or below each black amount composed of device independent color signals corresponding to the output device color signal equal to the total color material amount limit value. It is explanatory drawing of an example of a change when the amount of blacks of a side outline is changed. It is explanatory drawing of an example of the color gamut outline and lower side outline of a CMYK output device to which 240% was uniformly imposed as the total color material amount limit value in the device independent color space. It is a graph which shows an example of the relationship between the gradation of the process black of the target device in a prior art, and the coverage of each color component in an output device.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Target device order conversion part, 12 ... Color gamut mapping part, 13 ... Optimum black amount determination part, 14 ... Output device reverse conversion part, 21 ... Appropriate virtual surface device color signal group creation part, 22 ... Appropriate black amount calculation model Creation unit, 23 ... appropriate black amount calculation unit, 24 ... optimum black amount calculation unit, 31 ... program, 32 ... computer, 41 ... magneto-optical disk, 42 ... optical disk, 43 ... magnetic disk, 44 ... memory, 51 ... magneto-optical Disk device, 52... Optical disk device, 53.

Claims (22)

  The output device color in the output device in the M (M ≧ 4) dimensional color space including the black in which the restriction on the total amount of the color material is imposed from the target device color signal in the target device in the N (N ≧ 4) dimensional color space including the black In the color conversion device for converting to a signal, an appropriate total amount limit value is determined for each black amount so that the upper limit value of the total amount of color material excluding black in the output device is constant, and the appropriate total amount limit value for each black amount is determined. Based on the appropriate black amount calculating means based on the device independent color signal of the target device, the output from the appropriate black amount calculated by the appropriate black amount calculating means and the black amount of the target device color signal A color conversion apparatus comprising an optimum black amount calculation means for calculating a black amount of a device color signal.   The appropriate black amount calculation means is a lower side constituting the lower outline corresponding to the black amount from the appropriate total amount limit value for each black amount set so that the upper limit value of the total amount of color materials excluding black is constant. Appropriate virtual surface device color signal group generating means for generating an outer surface device color signal, a corresponding device independent color signal is calculated from the lower outer surface device color signal, and the device independent color signal and the device independent signal belong to it. A black amount calculation model creating means for creating a model for calculating a proper black amount from a black amount of a lower outer surface is provided, and the proper black amount is calculated using the model. Item 2. The color conversion device according to Item 1.   The output device color in the output device in the M (M ≧ 4) dimensional color space including the black in which the restriction on the total amount of the color material is imposed from the target device color signal in the target device in the N (N ≧ 4) dimensional color space including the black In the color conversion device for converting to a signal, target device forward conversion means for converting the target device color signal into a device independent color signal in a device independent color space, and from the black amount of the device independent color signal and the target device color signal An optimum black amount determining means for calculating the black amount of the output device color signal, the output device color signal from the device independent color signal and the black amount of the output device color signal calculated by the optimum black amount determining means. Output device reverse conversion means for calculating, and the optimum black amount determining means is configured so that the upper limit value of the total amount of color materials excluding black is constant. An appropriate total amount limit value is calculated for each amount, and a lower outer surface device color signal constituting a lower outer surface in the device color space of the output device corresponding to the black amount is created from the appropriate total amount limit value for each black amount An appropriate virtual surface device color signal group creating means; calculating a corresponding device independent color signal from the lower outer surface device color signal; and a black amount of the lower outer surface to which the device independent signal belongs. A black amount calculation model creating unit for creating a model for calculating an appropriate black amount corresponding to a device independent color signal from the device independent color signal using the model created by the black amount calculation model creating unit. A color conversion apparatus that calculates an appropriate black amount and calculates the black amount of the output device color signal from the appropriate black amount and the black amount of the target device color signal.   The output device color in the output device in the M (M ≧ 4) dimensional color space including the black in which the restriction on the total amount of the color material is imposed from the target device color signal in the target device in the N (N ≧ 4) dimensional color space including the black In the color conversion device for converting to a signal, target device forward conversion means for converting the target device color signal into a device independent color signal in a device independent color space, and from the black amount of the device independent color signal and the target device color signal An optimum black amount determining means for calculating the black amount of the output device color signal, the output device color signal from the device independent color signal and the black amount of the output device color signal calculated by the optimum black amount determining means. Output device reverse conversion means for calculating, and the optimum black amount determining means is configured so that the upper limit value of the total amount of color materials excluding black is constant. A proper total amount limit value for each black amount on the achromatic color reference line set near the achromatic color axis in the vice independent color space is calculated, and the appropriate total amount limit value for each black amount on the achromatic color reference line is used as a reference. An appropriate total amount limit value for each black amount other than the achromatic reference line is determined so that the total amount limit value monotonously increases as the color gamut outline limited to the black amount is approached, and the black amount is determined from the appropriate total amount limit value for each black amount. Appropriate virtual plane device color signal group creating means for creating a device color signal constituting the lower outline in the device color space of the output device corresponding to the quantity, and a device independent color signal corresponding from the lower outline plane device color signal The black amount calculation model for creating a model for calculating the appropriate black amount corresponding to the device independent color signal from the device independent color signal and the black amount of the lower outer surface to which the device independent signal belongs And calculating the appropriate black amount from the device independent color signal using the model created by the black amount calculation model creating unit and outputting the black amount from the appropriate black amount and the black amount of the target device color signal. A color conversion apparatus characterized by calculating a black amount of a device color signal.   The color conversion apparatus according to claim 4, wherein the achromatic color reference line is a color signal group in a device-independent color space corresponding to process black in the target device or the output device.   The color conversion apparatus according to claim 4, wherein the achromatic color reference line is a lightness axis in a device-independent color space.   The optimum black amount determination unit creates a lower outer surface device color signal by a virtual surface device color signal group generation unit for each black amount in the target device, and generates a device based on the lower outer surface device color signal. A model for calculating an appropriate black amount corresponding to an independent color signal is created by a black amount calculation model creating means, and a model corresponding to the black amount of the target device color signal from a model created for each black amount in the target device The color conversion apparatus according to claim 3, wherein the appropriate black amount is calculated by selecting and using the color.   The optimum black amount determining means generates the lower outline surface device color signal corresponding to a certain black amount in the target device by the virtual surface device color signal group creating means, and at the time of the black amount in the target device A color material that obtains the minimum black amount that is the minimum black amount of the output device necessary to reproduce the color gamut of the target device color signal in a device-independent color space, and excludes black at the minimum black amount An appropriate total amount limit value is calculated for each black amount of the output device so that the upper limit value is constant, and the black amount is calculated from the appropriate total amount limit value for each black amount of the output device. The color conversion apparatus according to claim 7, wherein a lower outline surface device color signal that constitutes a lower outline surface in a device color space of an output device corresponding to is generated.   The appropriate virtual surface device color signal group creating means sets the upper limit value of the total amount of color material excluding black to be constant as a value obtained by subtracting 100% from the limit value of the total amount of color material imposed on the output device. The color conversion device according to claim 2, wherein the color conversion device is a color conversion device.   The appropriate virtual surface device color signal group generation means monotonically increases as the ink decreases from 0% when the ink is 100%, and the ink becomes 0 from the upper limit of the total amount of the color material excluding the ink to be made constant. 10. The appropriate total amount limit value for each black amount is calculated by subtracting a predetermined margin that becomes a maximum value at the time of%. 10. Color conversion device.   The output device color in the output device in the M (M ≧ 4) dimensional color space including the black in which the restriction on the total amount of the color material is imposed from the target device color signal in the target device in the N (N ≧ 4) dimensional color space including the black In the color conversion method for converting to a signal, an appropriate total amount limit value is determined for each black amount so that the upper limit value of the total amount of color material excluding black in the output device is constant, and the appropriate amount for each determined black amount Based on the total amount limit value, the appropriate black amount is calculated from the device independent color signal of the target device by the appropriate black amount calculating means, and the output device color signal is calculated from the calculated appropriate black amount and the black amount of the target device color signal. A color conversion method characterized in that the black amount of ink is calculated by an optimum black amount calculation means.   The lower outer surface device color signal that constitutes the lower outer surface corresponding to the black amount is appropriately virtualized from the appropriate total amount limit value for each black amount set so that the upper limit value of the total amount of color materials excluding black is constant. A surface device color signal group creating means, calculating a corresponding device independent color signal from the lower outer surface device color signal, and calculating the device independent color signal and the black amount of the lower outer surface to which the device independent signal belongs. 12. A model for calculating an appropriate black amount from a black amount is created by a black amount calculation model creating unit, and the appropriate black amount is calculated by the appropriate black amount calculating unit using the model. The color conversion method described.   The output device color in the output device in the M (M ≧ 4) dimensional color space including the black in which the restriction on the total amount of the color material is imposed from the target device color signal in the target device in the N (N ≧ 4) dimensional color space including the black In the color conversion method for converting into a signal, the target device color signal is converted into a device independent color signal in a device independent color space by a target device forward conversion unit, and the device independent color signal and the black amount of the target device color signal are calculated. The black amount of the output device color signal is calculated by the optimum black amount determining means, and the output device color signal is calculated by the output device inverse converting means from the calculated black amount of the output device color signal and the device independent color signal The black amount of the output device color signal is calculated so that the upper limit of the total amount of color materials excluding black is constant. The appropriate total amount limit value is calculated and the lower outer surface device color signal constituting the lower outer surface in the device color space of the output device corresponding to the black amount is calculated from the appropriate total amount limit value for each black amount. Created by a device color signal group creation means, calculates a corresponding device independent color signal from the lower outer surface device color signal, and based on the device independent color signal and the black amount of the lower outer surface to which the device independent signal belongs A model for calculating an appropriate black amount corresponding to a device-independent color signal is created by the black amount calculation model creating means, and the appropriate black amount is calculated from the device-independent color signal using the created model. A color conversion method comprising: calculating a black amount of the output device color signal from a black amount of the target device color signal.   The output device color in the output device in the M (M ≧ 4) dimensional color space including the black in which the restriction on the total amount of the color material is imposed from the target device color signal in the target device in the N (N ≧ 4) dimensional color space including the black In the color conversion method for converting into a signal, the target device color signal is converted into a device independent color signal in a device independent color space by a target device forward conversion unit, and the device independent color signal and the black amount of the target device color signal are calculated. The black amount of the output device color signal is calculated by the optimum black amount determining means, and the output device color signal is calculated by the output device inverse converting means from the calculated black amount of the output device color signal and the device independent color signal The black amount of the output device color signal is calculated so that the upper limit of the total amount of color materials excluding black is constant. Calculate the appropriate total amount limit value for each black amount on the achromatic color reference line set in the vicinity of the achromatic color axis in an independent color space, and use the appropriate total amount limit value for each black amount on the achromatic color reference line as a reference The appropriate total amount limit value for each black amount other than the achromatic color reference line is determined so that the total amount limit value monotonously increases as the color gamut outline limited to the black amount to be applied, and the appropriate total amount limit value for each black amount is determined. The device color signal constituting the lower outline in the device color space of the output device corresponding to the black amount is created by the appropriate virtual plane device color signal group creation means, and the corresponding device independent from the lower outline device color signal A black amount calculation model creating means generates a model for calculating an appropriate black amount corresponding to a device independent color signal from the device independent color signal and the black amount of the lower outer surface to which the device independent signal belongs. And calculating the appropriate black amount from the device independent color signal using the created model, and calculating the black amount of the output device color signal from the appropriate black amount and the black amount of the target device color signal. A color conversion method characterized by the above.   The color conversion method according to claim 14, wherein the achromatic reference line is a color signal group in a device-independent color space corresponding to process black in the target device or the output device.   The color conversion method according to claim 14, wherein the achromatic color reference line is a lightness axis in a device-independent color space.   For the calculation of the black amount of the output device color signal, for each black amount in the target device, a lower outer surface device color signal is generated by a virtual surface device color signal group creating means, and the lower outer surface device color signal is generated. A model for calculating the appropriate black amount corresponding to the device independent color signal is created by the black amount calculation model creating means, and the black amount of the target device color signal is generated from the model created for each black amount in the target device. Selecting and using a model corresponding to the above, calculating the appropriate black amount, and calculating the black amount of the output device color signal from the appropriate black amount and the black amount of the target device color signal. The color conversion method according to any one of claims 13 to 16.   When creating a lower outline surface device color signal corresponding to a certain black amount in the target device, the color gamut in the device-independent color space of the target device color signal is reproduced at the black amount in the target device The minimum black amount, which is the minimum black amount of the output device necessary for the output, is obtained, and the upper limit value of the total amount of the color material excluding black at the minimum black amount is obtained so that the upper limit value becomes constant. And calculating an appropriate total amount limit value for each black amount of the output device, and constructing a lower outline in the device color space of the output device corresponding to the black amount from the appropriate total amount limit value for each black amount of the output device The color conversion method according to claim 17, wherein a lower outline device color signal is created.   19. The upper limit value of the total amount of color material excluding black to be made constant is a value obtained by subtracting 100% from the limit value of the total amount of color material imposed on the output device. The color conversion method according to any one of the above.   Predetermined from the upper limit of the total amount of color material excluding black to be constant, monotonically increasing as the ink decreases at 0% when the ink is 100% and maximum when the ink is 0% 20. The color conversion method according to claim 12, wherein the appropriate total amount limit value for each black amount is calculated by subtracting the margin obtained.   The output device color in the output device in the M (M ≧ 4) dimensional color space including the black in which the restriction on the total amount of the color material is imposed from the target device color signal in the target device in the N (N ≧ 4) dimensional color space including the black A color conversion program for executing a color conversion process for conversion into a signal, wherein the color conversion device functions as claimed in any one of claims 1 to 10 or any one of claims 11 to 20. A color conversion program that causes a computer to execute the color conversion method described in 1.   The output device color in the output device in the M (M ≧ 4) dimensional color space including the black in which the restriction on the total amount of the color material is imposed from the target device color signal in the target device in the N (N ≧ 4) dimensional color space including the black The function of the color conversion device according to any one of claims 1 to 10 or the claims 11 to 11 in a computer-readable storage medium storing a color conversion program for executing a color conversion process for converting to a signal. A computer-readable storage medium storing a color conversion program that causes a computer to execute the color conversion method according to any one of items 20.

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