JP3995735B2 - Color prediction formula creation apparatus and color prediction formula creation method - Google Patents

Description

[0001]
[Technical field to which the invention belongs]
The present invention relates to a color prediction formula creation apparatus that constructs a color prediction formula for predicting an output color when color image information is transferred between devices such as CRTs, color printers, and color copies having different color reproduction ranges. Specifically, if the total amount of CMYK four color inks (or toners) in the color patch exceeds the maximum printable amount, the black ink remains constant and the cyan, magenta, and yellow ink amounts are reduced. The present invention relates to a color prediction formula creation apparatus and a color prediction formula creation method for correcting the output of a color patch so that each color patch does not exceed a predetermined total ink amount.
[0002]
[Prior art]
In recent years, media handling color images have been developed in various forms. For example, a system is known in which characters and images are read by a color scanner, edited and processed on a computer display, and the result is printed out by a color printer or the like. However, in this case, the colors reproduced on the display and the colors printed out may be different from each other due to differences in color reproduction methods, color mixing systems (RGB, YMC), and color reproduction range mismatches. It is well known.
[0003]
For this reason, color management systems using device-independent colors have been studied with the aim of achieving simple and accurate color reproduction between different color input / output devices (devices). This system aims at color reproduction that is colorimetrically consistent among various devices by using intermediate color signals independent of the devices.
[0004]
In general, as a color signal independent of a device, a signal suitable for human visual characteristics such as an XYZ signal or an L ^* a ^* b ^* signal of a 1931 color system defined by the CIE (International Commission on Illumination) is used.
[0005]
In order to perform colorimetrically consistent color reproduction as described above, it is necessary to grasp the relationship between device signals and colorimetric values. Therefore, a color prediction formula for predicting a colorimetric value for an arbitrary device signal is often constructed based on a combination of a small number of device signals and colorimetric values.
[0006]
For example, when creating a color prediction formula for a CMYK (CMY) printer, a plurality of color patches composed of various combinations of CMYK (CMY) signals are output by the printer, and standard signals (for example, CIE L ^* a) corresponding to each color patch are output. ^* b ^* signal, XYZ signal) is obtained by colorimetry, and a color prediction formula is created from the correspondence between the color patch output value CMYK (CMY) and the colorimetric value. C is cyan, M is magenta, Y is yellow, and K is black.
[0007]
Further, as reference technical documents related to these, for example, Japanese Patent Laid-Open Nos. 63-254887, 2-86388, and 6-350844 are disclosed.
[0008]
In the embodiment disclosed in Japanese Patent Laid-Open No. Hei 6-350844, patches of 11 stages of CMY colors, a total of 1331 (= 11 × 11 × 11) colors are output, and a prediction formula (multiple regression reproduction color prediction model formula) is created. ing.
[0009]
In Japanese Patent Laid-Open No. 63-254887, the number of output patches is reduced by changing the number of signals used for the combination of CMY, which are output signals of color patches, according to the color components.
[0010]
Furthermore, in the color patch creation method disclosed in Japanese Patent Laid-Open No. 2-86388, the efficiency is improved by reducing the number of patches as the density of K increases with respect to the CMYK printer.
[0011]
By the way, in order to create a highly reliable color prediction formula, it is desirable to output as many color patches as possible and perform color prediction based on the color measurement results. However, if a CMYK printer or the like tries to output, for example, eight color patches for each color, the total number of patches reaches 4096 patches, and the burden required for color measurement work becomes very large. For this reason, in the past, there were many devices that focused on reducing the number of patches as much as possible.
[0012]
On the other hand, some color printers have a limit on the amount of ink that can be printed at the same position. For example, in the case of an electrophotographic printer, if the total amount of CMYK ink (total toner adhesion amount) is too large, the ink (toner) will cause a transfer failure or a fixing failure on the recording paper, resulting in significant color unevenness. Will occur.
[0013]
Also in the case of an ink jet printer, if the amount of ink is too large, the ink may not be properly absorbed (thrown) onto the recording paper and may bleed.
[0014]
[Problems to be solved by the invention]
However, in the conventional techniques as described above, since the total amount of ink of the printer is not taken into consideration, a color patch that exceeds the constraint condition of the total amount of ink is output.
[0015]
That is, even if a color patch that exceeds the total ink amount restriction is output to a printer that has a restriction on the total ink amount of CMYK, stable color reproduction cannot be performed as the printer. Therefore, if a color prediction formula is created using color measurement data of a color patch exceeding the total ink amount regulation, the prediction formula becomes very unreliable.
[0016]
In particular, a color patch having a large total ink amount concentrates in a low lightness region, and thus there is a problem that a printer signal corresponding to a colorimetric signal in the low lightness region cannot be obtained correctly.
[0017]
Another possible method is to create a color prediction formula after deleting colorimetric data that exceeds the total amount of ink, but in this case, the number of effective color patches decreases and the prediction accuracy decreases. was there.
[0018]
The present invention has been made in view of the above, and an object of the present invention is to realize color patch output for creating a highly reliable color prediction formula even when there is a restriction on the total amount of ink in the printer. To do.
[0019]
[Means for Solving the Problems]
In order to achieve the above object, in the color prediction creation apparatus according to claim 1, the device signal is converted into a color value from the colorimetric result of the color patch composed of a plurality of color materials output by the output device. A color prediction creation device for conversion, wherein when outputting the color patch, a color patch for which the total amount of color material exceeds the limit is controlled so as not to exceed the limit. Using the patch generation means, the image forming means for outputting the color patch, the color measurement means for measuring the color patch, the color measurement result and the device signal, a color value reproduced from the device signal is obtained. Color prediction formula creation means for creating a model formula to be predicted, and the color patch generation means makes the black color material amount constant when the total amount of color material of each color patch exceeds the maximum amount, and other than black each colorant amount of those reducing A.
[0020]
That is, when a plurality of color patches are output by a color image recording apparatus, the total amount of ink is limited by correcting the output value of the color patch so that each color patch does not exceed a predetermined total amount of ink. Even in a printer that is capable of outputting appropriate color patches, a reliable color prediction formula is constructed. In particular, for color patches where the total ink amount exceeds the limit, processing is performed to reduce the ink amounts of cyan, magenta, and yellow while keeping the black ink amount constant, so the lightness is low Patch data can be converted without reducing color patches, and a highly accurate color prediction model is constructed in the low lightness range.
[0023]
In the color prediction creation apparatus according to claim 2 , the color material is toner or ink.
[0024]
That is, by using toner or ink as the color material, it is possible to provide a color prediction formula in an image forming apparatus such as a color printer that uses ink or a copier that forms a color image using toner.
The color prediction creation method according to claim 3 is a color prediction creation method for converting a device signal into a color value from a color measurement result of a color patch composed of a plurality of color materials output by an output device. A color patch generating step of generating a color patch by controlling the color patch so that the total amount of color material exceeds a limit when the color patch is output; Using the image forming process for outputting the patch, the color measurement process for measuring the color patch, the color measurement result and the device signal, a model formula for predicting the color value reproduced from the device signal is created. A color prediction formula creation step, wherein the color patch generation step makes the amount of black color material constant when the total amount of color material of each color patch exceeds the maximum amount, and reduces the amount of each color material other than black It is.
That is, when a plurality of color patches are output by a color image recording apparatus, the total amount of ink is limited by correcting the output value of the color patch so that each color patch does not exceed a predetermined total amount of ink. Even in a printer that is capable of outputting appropriate color patches, a reliable color prediction formula is constructed. In particular, for color patches where the total ink amount exceeds the limit, processing is performed to reduce the ink amounts of cyan, magenta, and yellow while keeping the black ink amount constant, so the lightness is low Patch data can be converted without reducing color patches, and a highly accurate color prediction model is constructed in the low lightness range .
In the color prediction creation method according to claim 4 , the color material is toner or ink.
That is, by using toner or ink as the color material, it is possible to provide a color prediction formula in an image forming apparatus such as a color printer that uses ink or a copier that forms a color image using toner.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
[0026]
Embodiment
(Configuration of the embodiment)
FIG. 1 is a block diagram showing a configuration of a color matching system according to an embodiment, and has a function for colorimetrically matching an image on a monitor and an output image by a printer.
[0027]
That is, this color matching system includes a color monitor 101 for displaying a color image on a monitor, a monitor profile 102 in which a data file describing color conversion parameter characteristics of the color monitor 101 is stored, a monitor profile Based on the color conversion parameters prepared in 102, for example, a color conversion unit (1) 103 that converts RGB signals into XYZ tristimulus values and a color output that is output from the color monitor 101 that has undergone color conversion are output to a printer. Based on the printer 104, the printer profile 105 storing the data file describing the color conversion parameter characteristics of the color printer 104, and the color conversion parameters prepared in the printer profile 105, for example, XYZ tristimulus Convert value to CMYK And a conversion unit (2) 106..
[0028]
FIG. 2 is a block diagram illustrating an example of a color prediction expression creation system according to the embodiment. In the figure, 201 is an output sample output by the color printer 104, 202 is a colorimeter that measures the color of the output sample 201, and 203 is a colorimetric value that stores each value measured by the colorimeter 202. 204, an output value storage device for storing values such as CMYK whose output values are known in advance, and 205 for color reproduction based on the output values of the storage device 204 and the colorimetric values of the storage device 203. This is a color prediction formula determination device that constructs a prediction formula and outputs the color prediction formula.
[0029]
FIG. 3 is a block diagram illustrating a configuration of the color patch generation unit according to the embodiment. In the figure, a color patch generation unit 300 serving as a color patch generation unit includes an ink amount conversion unit 301 that converts color patch data into an ink amount assuming a printer with no ink amount restriction, and the converted ink amount. Based on the output results of the total ink amount check unit 302 that checks the total amount, the patch data conversion unit 303 that executes conversion processing so that the patch data does not exceed the total ink amount, and the output result of the total ink amount check unit 302 And a selector 304 that selects / outputs whether to output the data as-is or to output the patch data converted by the patch data conversion unit 303.
(Operation of the embodiment)
Next, the operation in the above configuration will be described. First, in the color matching system shown in FIG. 1, in order to make a colorimetric match between the image on the color monitor 101 and the output image from the color printer 104, a device is provided for each of the monitor profile 102 and the printer profile 105. A data file describing the characteristics is prepared, and color conversion between the color monitor 101 and the color printer 104 is performed using device-independent color signals such as XYZ tristimulus values based on this information. Execute.
[0031]
For this color conversion, generally used, for example, matrix calculation or interpolation calculation is used.
[0032]
In the color matching system as described above, it is important to accurately obtain the color conversion parameters described in the monitor profile 102 and the printer profile 105 in order to realize highly accurate color conversion.
[0033]
In general, to create a color conversion parameter:
(1) Output of predetermined color patch and color measurement (2) Color prediction formula creation based on color measurement result (3) Construction of color conversion parameter using color prediction formula is taken.
[0034]
In FIG. 2, first, an output pattern including a plurality of color patches whose output data such as C, M, Y, and K are known in advance is prepared. The C, M, Y, and K output data are stored in the output value storage device 204.
[0035]
Next, the data is output by an output device (color printer 104) that targets the output pattern. Further, the color patch in the output sample 201 is measured by the colorimeter 202, and the colorimetric value is stored in the colorimetric value storage device 203.
[0036]
Then, values stored in the output value storage device 204 and the colorimetric value storage device 203 are read out, and a color prediction formula is determined by the color prediction formula determination device 205 based on the values.
[0037]
This color prediction formula is a model formula for efficiently calculating color conversion parameters on a computer, and means, for example, a conversion function for predicting color values (Lab values, etc.) actually reproduced from the printer output signal CMYK. is doing. As a color reproduction prediction method, a generally known multi-order polynomial, a memory map interpolation method, a neural network, or the like is used.
[0038]
Next, parameters used for actual color conversion are created based on the color prediction formula created by the color prediction formula decision unit 205. In actual color conversion, conversion parameters from color values to printer signals are required.
[0039]
That is,
Color prediction formula: (L, a, b) = f (c, m, y, k)
Is used to determine the coefficient of the color conversion g () such that (c, m, y, k) = g (L, a, b).
[0040]
In the case of a four-color printer, since four-input three-output conversion is performed, the optimum parameter cannot be uniquely determined. Therefore, usually some constraint condition is set, and the conversion parameter of K (black) is set, and then the variable parameters for the remaining c, m, and y are determined. The variable parameters for c, m, and y are set based on the minimum color difference.
[0041]
In the creation of the color conversion parameter described above, what color patch is output greatly affects the reliability of the predicted color. Therefore, in the color patch output in the present embodiment, an appropriate color patch is output even in a printer having a restriction on the total amount of ink. The output method will be described below.
[0042]
Here, a description will be given by taking a four-color printer as an example in which an output with a total ink amount of up to 300% is guaranteed. That is,
(I (c) + I (m) + I (y) + I (k)) <300%
I (x) indicates the ink amount at the time of the output signal x.
[0043]
The printer is assumed to be a printer having 256 gradations for each color. The relationship between the printer output signal and the ink amount varies depending on the image forming process of the printer and its conditions, but for simplicity, the CMYK output signal and the ink amount have a linear relationship as shown in the following equation. Assume that there is.
[0044]
That is,
(Ink amount) = (output signal) × 100/255
It is.
[0045]
In FIG. 3, first, the color patch generation unit 300 generates color patch data assuming a printer with no ink amount restriction.
[0046]
For example, if five levels of gradation output [0, 64, 128, 192, 255] are set for each color, the total number of output patches is
5 × 5 × 5 × 5 = 625 (patch)
It becomes.
[0047]
However, this 625 patch pattern includes a patch that exceeds the total ink amount restriction. For example,
[C, M, Y, K] = [255, 255, 255, 255]
In the case of such a color patch, the total ink amount reaches 400% (= 100 + 100 + 100 + 100), and as a result, 35 patches out of 625 patches exceed the total ink amount 300% and are wasted. Become.
[0048]
Therefore, a conversion process is applied to the patch having a too large total ink amount, and the control is performed so that the total ink amount does not exceed the limit.
[0049]
That is, if the converted ink amounts of C, M, Y, and K are I ′ (c), I ′ (m), I ′ (y), and I ′ (k),
t = (MAX_INK_I (k)) / (I (c) + I (m) + I (y))
I ′ (c) = t × I (c)
I ′ (m) = t × I (m)
I ′ (y) = t × I (y)
I ′ (k) = I (k)
It becomes.
[0050]
Here, the k (black) ink amount is not converted because if the output value of k is reduced in the same manner as c, m, and y, the number of low-lightness color patches is reduced, and as a result. This is to prevent the color prediction accuracy in the low brightness range from being lowered.
[0051]
For the same reason, a method of increasing the ink amount of k (black) and reducing the ink amount of c, m, and y by that amount can be considered.
[0052]
For example,
t = (MAX_INK_I (k) × α (k)) / (I (c) + I (m) + I (y))
I ′ (c) = t × I (c)
I ′ (m) = t × I (m)
I ′ (y) = t × I (y)
I ′ (k) = I (k) × α (k)
And
[0053]
Where α (k) is for all k
α (k) × I (k) <100
α (k) ≧ 1.0
It is a variable that satisfies
[0054]
Therefore, by applying the conversion processing described above to the output data of the color patch and executing the patch output, it is possible to output a color patch with an appropriate total amount of ink so that all the color patch data can be used effectively. become.
[0055]
In the above embodiment, the construction example of the color prediction formula for predicting the output color in the color printer 104 has been described. However, other parameters for color conversion such as a digital color copying machine and a color printer are also described. It can be applied to the calculation of
[0056]
【The invention's effect】
As described above, according to the color prediction creation apparatus (claim 1) of the present invention, when a plurality of color patches are output by the color image recording apparatus, each color patch does not exceed a predetermined total ink amount. By outputting after correcting the output value of the color patch, an appropriate color patch is output even in a printer in which the total amount of ink is limited, so that a highly reliable color prediction formula can be constructed. In particular, for color patches where the total ink amount exceeds the limit, processing is performed to reduce the ink amounts of cyan, magenta, and yellow while keeping the black ink amount constant, so the lightness is low Patch data can be converted without reducing color patches, and a highly accurate color prediction model is constructed in the low lightness range.
[0058]
Further, according to the color prediction creating apparatus according to the present invention (Claim 2), Oite to claim 1, by said toner or ink color materials, a color image by a color printer or toner used, for example ink A color prediction formula in an image forming apparatus such as a copying machine to be formed can be provided.
Further, according to the color prediction creation method according to the present invention (claim 3 ), when a plurality of color patches are output by the color image recording apparatus, the output of the color patches is performed so that each color patch does not exceed a predetermined total ink amount. By outputting after correcting the value, an appropriate color patch can be output even in a printer in which the total amount of ink is limited, so that a highly reliable color prediction formula is constructed. In particular, for color patches where the total ink amount exceeds the limit, processing is performed to reduce the ink amounts of cyan, magenta, and yellow while keeping the black ink amount constant, so the lightness is low Patch data can be converted without reducing color patches, and a highly accurate color prediction model is constructed in the low lightness range .
Further, according to the color prediction creation method according to the present invention (claim 4 ), in claim 3 , for example, a color printer using ink or a color image using toner is formed by using the color material as toner or ink. A color prediction formula in an image forming apparatus such as a copying machine can be provided.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a color matching system according to an embodiment.
FIG. 2 is a block diagram illustrating an example of a color prediction expression creation system according to an embodiment.
FIG. 3 is a block diagram illustrating a configuration of a color patch generation unit according to the embodiment.
[Explanation of symbols]
104 Color Printer 201 Output Sample 202 Colorimeter 203 Colorimetric Value Storage Device 204 Output Value Storage Device 205 Color Prediction Formula Determination Device 300 Color Patch Generation Unit 302 Total Ink Amount Check Unit 303 Patch Data Conversion Unit

Claims (4)

A color prediction creation device that converts a device signal into a color value from a color measurement result of a color patch composed of multiple color materials output by an output device,
Color patch generation means for generating a color patch by controlling the color patch so that the total amount of the color material exceeds the limit when the color patch is output;
Image forming means for outputting the color patch;
A colorimetric means for measuring the color patch;
A color prediction formula creating means for creating a model formula for predicting a color value reproduced from the device signal using the color measurement result and the device signal;
Have
The color patch generation device, wherein the color patch generation means makes the amount of black color material constant when the total amount of color material of each color patch exceeds the maximum amount, and reduces the amount of each color material other than black.   The color prediction creation apparatus according to claim 1, wherein the color material is toner or ink. A color prediction creation method for converting a device signal into a color value from a color measurement result of a color patch composed of multiple color materials output by an output device,
A color patch generation step of generating a color patch by controlling the color patch so that the total amount of color materials exceeds the limit when the color patch is output, so as not to exceed the limit;
An image forming step of outputting the color patch;
A colorimetric process for measuring the color patch;
A color prediction formula creating step for creating a model formula for predicting a color value reproduced from the device signal using the color measurement result and the device signal;
Have
In the color patch generation step, when the total amount of color materials of each color patch exceeds the maximum amount, the color material amount of black is made constant, and the amount of each color material other than black is reduced. The color prediction creation method according to claim 3, wherein the color material is toner or ink.

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