JPH0376633B2 - - Google Patents

Description

[Detailed Description of the Invention] Conventionally, in order to create printed matter, image information is captured from a color original, and C (cyan), M (magenta), Y (yellow), and Bk (black) are used for printing based on the image information. ) Calculate the dot area ratio of each plate and output a halftone film for each plate, or engrave the printing plate for each plate using a mechanical engraving method, laser engraving method, etc. to create a gravure printing plate. There are known devices for creating.
In such a device, image information is stored in a storage device, and the arrangement of the images can be freely set, the color of a part or a specific part of the image can be modified or changed, or the color of a specified part or part of the image can be modified or changed. There are products on the market that allow you to arrange specified colors on parts in a specified manner. A typical example of such a device is what is commonly called a layout scanner. Devices such as such layout scanners are used to reproduce colors of image information.

When changing or setting the color of a certain part in a device such as the layout scanner, a color to be changed or a color to be set may be specified. In such a case, if the color is specified by the dot area ratio, it is sufficient to key in the value and there will be no problem. However, a problem arises when colors are specified using color samples.

In this way, when a color is designated by a color sample, the following method can be considered as a method of inputting information on that color in the form of a halftone area ratio to a device such as a layout scanner.

For example, assume that a printing layout sheet has a large number of color samples attached to it for specifying colors. For example, suppose you want to uniformly fill a background with a certain color, and a small piece of paper with the background color is attached as a color sample.

When printing a specified area with the same color as this color sample, to determine what halftone area ratio to print each CMYBk plate, set the halftone area ratio at approximately 10% intervals from this color sample. Visually compare the printed color charts with the different colors and select the one that is most similar. It is common to make a decision using what is written and input it into the device. However, this method has the disadvantage that it takes time to make the comparison, and the colors selected from the color chart vary depending on the person, so that the determined halftone area ratio tends to vary. Accurately specifying the dot area ratio requires an experienced veteran, but even then it is not perfect.

On the other hand, reflection densitometers that can measure the density of an object to be measured and calculate the dot area ratio are currently on the market. In this densitometer, the measured density value is processed by a microcomputer built into the densitometer to calculate the dot area ratio. The Yule-Nielsen equation is usually used to calculate the dot area ratio from this density value. In order to use this Yule-Nielsen equation, measure the standard density in advance and set the halftone area ratio of that part to the standard value (100%).
It is necessary to set the dot area ratio to , then actually measure the object to be measured for the halftone dot area ratio, and use the relationship with the reference density.

Therefore, it is only applicable to colors that have a standard density, and is usually used only for monochrome colors. Moreover, the Yule-Nielsen equation can be established by ideally reproducing halftone dots without dot gain, and by appropriately setting coefficients that vary depending on the screen frequency, density, and paper transparency. Therefore, in actual use, it is not possible to accurately obtain a wide range of dot area ratios from light areas to shadow areas even in monochromatic areas. Furthermore, it is extremely difficult to calculate the dot area ratio of secondary colors or higher.

Therefore, such a densitometer cannot display a combination of dot area ratios for each YMCBk version to express the color of the color sample.

Further, such conventionally known densitometers cannot display the combination of dot area ratios for each YMCBk version for the following reason. In other words, printing ink
YMC ink is not ideal; Y ink contains M and C components, M ink contains Y and C components, and C ink contains M and Y components. may be included. Since the YMC printing ink actually used is not ideal, the colors of the measured objects such as color samples are B (blue violet), G (green), and R (red), which are complementary colors of YMC. The concentration values obtained by measuring through each filter are
Even if the dot area ratio is calculated using Nielsen's formula, the value does not indicate the actually required dot area ratio of each positive YMC. This will be more clearly understood by the following example. For example, it is easier to understand if we assume that an image with a halftone dot area ratio of 100% is printed using only C ink from a certain ink manufacturer. If you calculate the density of this printed matter through an R filter, a G filter, and a B filter, you will get 1.53, 0.52, and 0.17, respectively.
It is clear that it cannot be used to determine the halftone area ratio of the Y version.

This becomes even more complicated when not only one color of ink but a plurality of color inks are to be overprinted. Therefore, such a densitometer cannot be used to determine the halftone dot area ratio of a printing plate of each color on which the color of the color sample is to be reproduced.

The present invention eliminates the various drawbacks described above, and when expressing any color using ink of each YMC color or each color of YMCBk, it is possible to determine the dot area ratio of each color plate. The purpose is to provide a device that can easily determine which combinations should be used.

That is, the present invention provides a color information-halftone area ratio conversion table showing the correspondence between color information and a combination of halftone area ratios corresponding to the color information of three color separations of YMC, and a color separation of Bk. a first storage means storing Bk plate calculation data indicating the correspondence between the halftone area ratio and the color information; a color measurement means for measuring the color of the object to be measured to obtain color information; a second storage unit for storing color information obtained by the color measuring means;
, and the halftone dot area of the Bk plate from the color information stored in the second storage means and the Bk plate calculation data stored in the first storage means based on preset conditions. Find the rate and calculate the corresponding Bk
subtracting the color information corresponding to the halftone area ratio of the plate from the color information stored in the second storage means;
a Bk plate halftone area ratio calculation means for calculating color information taking the Bk plate into consideration; a color information to halftone dot area ratio conversion table stored in the first storage means; and a color information to halftone dot area ratio conversion table stored in the second storage means. Color information and/or the Bk
The second color information is selected from among the color information in the halftone dot area ratio conversion table by comparing the color information with the plate taken into consideration.
The color information stored in the storage means of and/or the color information stored in the storage means of
a color information selection means for selecting the color information closest to the color information considering the Bk version; a combination of halftone area ratios corresponding to the color information selected by the color information selection means; and a combination of halftone area ratios of the Bk version; It is an object of the present invention to provide a halftone dot area ratio determining device characterized by comprising a halftone dot area ratio output means for outputting a halftone dot area ratio.

Note that as the color information, color density, chromaticity, etc. can be used as a reference. In the following, the case where color density is used will be mainly explained for simplicity, but the same process can be performed even when chromaticity or the like is used as color information. That is, it is well known that color density and chromaticity are used as one of the methods of expressing a certain color, that is, one of the color representation methods. The R (red), G (green), and B (blue violet) color systems are well known as color systems for color density.

The XYZ color system (CIE (1931)) is the color system for chromaticity.
XYZ color system) or L ^* a ^* b ^* color system (CIE1976 (L ^* a ^*
b ^* )−Color Space), etc. are known. In the XYZ color system, the chromaticities x, y, and z are as follows: The closeness (similarity) of the colors is the chromaticity difference ΔE
= [(Y ₁ - Y ₂ ) ² + (x ₁ - x ₂ ) ² + (y ₁ - y ₂ ) ² ] ^1/2 .

Furthermore, in the L ^* a ^* b ^* color system, the chromaticities L ^* , a ^* , b ^* are {L ^* = 116 (Y/Y ₀ ) ^1/3 −16 a ^* = 500 [(X/X ₀ ) ^{1 /3} - (Y/Y ₀ ) ^1/3 ] b ^* = 200 [(Y/Y ₀ ) ^1/3 - (Z/Z ₀ ) ^1/3 ] However, X, Y, Z are tristimulus values, ₀ , Y ₀ , Z ₀ are expressed as the tristimulus values of the illumination light source, and the closeness of two certain colors is expressed as the chromaticity difference ΔE = [(L ₁ ^* −L ₂ ^* ) ² + (a ₁ ^* −a ₂ ^* ) ₂ + (b ₁ ^* −b ₂ ^* ) ²
] ^1
/2 .

As described above, chromaticity and chromaticity difference are used to express colors and the closeness of colors.

The aforementioned color density and color density difference are also used as methods to express colors and color closeness, but it is more convenient to use chromaticity and chromaticity difference when handling colors numerically. In particular, the L ^* a ^* b ^* system is excellent for quantitatively handling colors that are close to those perceived by humans.

The present invention provides an apparatus that can measure the chromaticity, color density, etc. of the object to be measured and easily determine the halftone dot area ratio of each color plate when expressing the color of the object in print. This is what I am trying to do.

Next, the present invention will be explained in more detail with reference to the drawings.

FIG. 1 is a conceptual diagram of an apparatus according to the first invention of this application, in which color information and halftone area ratios corresponding to the color information of color separation plates of a plurality of colors are stored in a first storage means 10 in advance. A color information to halftone dot area ratio conversion table showing the correspondence with the combination of Bk color separations and Bk plate calculation data showing the correspondence between the halftone area ratio of the Bk color separation version and color information are stored. The color information data obtained by the color measuring means 20 for obtaining the color information data of the object to be measured is temporarily stored in the second storage means 30.
As the color information data stored in the second storage means 30, for example, three types of color densities obtained through each of the R filter, G filter, and B filter are used to combine the color densities of the object to be measured. This may be a combination of sets or chromaticity. Next, the color information selection means 40 selects the color information of the color information-dot area ratio conversion table stored in the first storage means 10 and the color information of the object to be measured stored in the second storage means 30. Alternatively, by comparing the color information that takes into account the Bk plate (described later), the color information of the object to be measured or the color information that takes the Bk plate (described later) is the best among the color information in the color information-dot area ratio conversion table. Select the closest one.

On the other hand, the Bk halftone area ratio calculation means 50 calculates the color information stored in the second storage means 30 and the color information stored in the first storage means 10 based on preset conditions.
The dot area ratio of the Bk plate is determined from the Bk plate calculation data stored in the Bk plate calculation data, and the color information corresponding to the dot area ratio of the Bk plate is calculated from the color information stored in the second storage means 30. This method calculates color information that takes the Bk version into consideration.

In this case, the processing by the Bk halftone area ratio calculation means 50 is to select the color information closest to the color information stored in the second storage means 30 by the color information selection means 40, and to select the color information closest to the color information stored in the second storage means 30, The calculation may be performed after determining the conditions for the Bk plate calculation based on the above, or alternatively, the conditions for the Bk plate calculation may be determined and the Bk dot area ratio is determined before the processing by the color information selection means 40. It is also possible to have the calculation means 50 perform the processing, and it is convenient to be able to switch which one to perform.

As described above, the Bk version halftone area ratio calculation means 50
After completing the processing in , the color information selection means 40
Accordingly, the color information closest to the color information considering the Bk plate is selected from the color information one halftone dot area ratio conversion table.

In this way, the combination of dot area ratios corresponding to the color information selected by the color information selection means 40 is interpolated by the interpolation means as necessary, and then outputted by the dot area ratio output means 60 which outputs the dot area ratio. be done.

As described above, when expressing the color of an object to be measured (for example, a color sample) by printing with printing ink, the halftone area ratio at which each color of ink should be printed is easily determined.

Figures 2a and b show an example of a color information to halftone dot area ratio conversion table when color density is adopted as the color information, and the left side shows R. The combinations of color densities obtained through the filter, G filter, and B filter are shown, and the right side shows Y, M, and C, which correspond to the color density combinations shown on the left side.
The combinations of dot area ratios of the three color separations are shown.

Such a color density to halftone dot area ratio conversion table is created as follows. First, YM on printing paper
Using each ink of C., the dot area ratio is 0% to 100.
% at appropriate intervals, for example, at 10% intervals as in the case of FIG. 2, and actually prints to create a color chart. That is, in the example in Figure 2, for numbers 1 to 11, the MY version has a halftone area ratio of 0%, and only the C version has a halftone dot area ratio of 0% to 100%, changing in 10% increments, and for numbers 12 to 11, the dot area ratio is 0%. up to number 22
The Y. version has a halftone area ratio of ~%, and the halftone area ratio of the M version is 10.
%, and only the C plate is changed from 10% to 100% in 10% increments.The following color charts are created with various combinations in which the halftone area ratio of each YMC plate is changed in 10% intervals. There is. Such combinations result in 11 ³ =1331 combinations when the dot area ratio is varied at 10% intervals for each version of YMC.

For each color of the color chart created as described above, the combination of color densities obtained through each of the R filter, G filter, and B filter is determined. As described above, a color density/halftone dot area ratio conversion table is created that shows the correspondence between combinations of color densities and corresponding combinations of halftone dot area ratios of plates of each color for various colors.

Further, FIG. 3 is stored in the first storage means.
This is a table showing the correspondence between the dot area ratio of the Bk plate and the color density through each RGB filter as an example of Bk plate calculation data.

This is also done in the same way as creating the color density - halftone dot area ratio conversion table.
After changing the R by % and actually printing.
It is obtained by measuring color density through each GB filter.

Note that the Bk version calculation data is not in the form of a table as shown in Figure 3, but a function that can be expressed in a graph as shown in Figure 4 using the method of least squares based on the data in the table. It may also be in the form of this function.

Although color density is generally measured using each of the RGB filters described above, an interference filter or the like having a peak in the absorption portion of the spectral reflection curve of the printing ink may also be used. The same filter used when creating the color density to halftone dot area ratio conversion table must be used when measuring the color density of the object to be measured.

Looking at the color density vs. halftone dot area ratio conversion table obtained as above, for example, for numbers 1 to 11 in Figure 2, the halftone dot area ratio of each version of MY is 0% and does not change. Although only the C version has changed, not only the color density through the R filter, which is the complementary color of C, but also the color density through the other GB amber filters has changed. This is C
This is because the ink contains not only the C component but also other color components.

This relationship holds true for other inks as well, and they contain other components. Therefore, when determining the dot area ratio of a certain object, it is necessary to take into account not only the color density through one filter but also the color density through other filters. The data of the color density/halftone dot area ratio conversion table and the data for Bk plate calculation are stored in the first storage means 10, and such storage means may be a magnetic disk, a floppy disk, a ROM, etc. as appropriate. things are used.

As described above, the first storage means 10 stores in advance the color information dot area ratio conversion table and the Bk plate calculation data.

The color measuring means 20 measures the color of the object to be measured to obtain color information, and FIG. 5 is a block diagram showing one embodiment thereof. The example in FIG. 5 shows an example in which color density is used as color information, and the object to be measured 1, such as a color sample, is irradiated by a light source 21, and the reflected light is passed through a filter 2.
2 to the photoelectric conversion element 23, where it is converted into an electrical signal. The filter 22 is the same as the one used when creating the color density/dot area ratio conversion table, and three types of filters, R filter, G filter, B filter, etc. are installed so that they can be converted. It is. In this case, the filter may be switched electrically or manually. In addition, in the example shown in Figure 5, the light from the light source is emitted from an angle of 45 degrees and is received directly above. It's okay.

The electrical signal generated by the photoelectric conversion element 23 is amplified by an amplifier 24, subjected to necessary correction by a correction circuit 25, subjected to logarithmic conversion processing by a logarithmic converter 26, and then converted from an analog signal to a digital signal by an A/D converter 27. is converted into color information, and is input and stored in the second storage means 30 as color density. The value of the electric signal can be checked on a display meter 28. Note that the display meter 28 may be placed after the A/D converter 27 to provide a digital display.

As described above, the object to be measured is measured for each filter to obtain color information of the object to be measured, and these are stored in the second storage means 30 as described above. As the second storage means 30, an appropriate one such as a RAM can be selected.

The color information selection means 40 selects, in part, the color information of the object to be measured stored in the second storage means 30 and the color information in the color information-dot area ratio conversion table stored in the first storage means 10; The method compares the color information and selects the one closest to the color information of the object from among the color information in the halftone dot area ratio conversion table.
The selection is made as follows. For example, when color density is used as color information, R of the object to be measured is
Let the color information obtained through the filter, G filter, and B filter be D _R , _DG , and _DB , respectively.
Also, the R filter, the G filter at the n-th number of the color density-dot area ratio conversion table as the color information-dot area ratio conversion table,
The color density through the B filter is T _R (n),
Let T _G (n) and T _B (n). Next, the combination of color densities D _R , D _G , D _B of the object to be measured and the combination T _R (n), T _G ( n), T _B (n) distance S _A (n)
The combination of color densities T _R (n), T _G that minimizes
(n) and T _B (n).

The distance SA (n) is [SA (n)] ² = T _R (n) - D _R ] ² + [T _G (n) - D _G ]
It is obtained from the relational expression ² + [T _B (n) - D _B ] ₂ .

The value of n that minimizes the distance SA(n) is [SA(n)]
² matches the minimum value of n. Therefore, using the above relational expression, select the combination of color densities in the color density-dot area ratio conversion table that minimizes [SA(n)] ² by sequentially changing the value of n from n = 1 to the end. By searching, you can find the value of n that minimizes SA(n). The combination of color densities in the color density-dot area ratio conversion table corresponding to n that minimizes SA(n) is determined as the one closest to the combination of color densities of the object to be measured, and the combination of color densities is Corresponding Y.
A combination of halftone area ratios for each version of MC is determined.

Even in this case, if [SA(n)] ² becomes zero during the search, in other words, during the search, the combination of color densities of the object to be measured and the color in the color density-dot area ratio conversion table If a matching density is found, the combination of halftone area ratios corresponding to the combination of color densities at the current value of n is the data to be sought, and the subsequent search may be discontinued.

Although color information is selected in the manner described above, the same process may be performed even when chromaticity or the like is employed in addition to color density as color information.

The combination of dot area ratios of each YMC version determined as described above is outputted by the dot area ratio output means 60. The dot area ratio output means is for outputting the determined dot area ratio, and may be a display, a printer, or the like.

The combination of halftone dot area ratios output as described above indicates the halftone dot area ratio of each plate, and depending on the combination of halftone dot area ratios output in this way, printing using ink of each color will result in a It is possible to obtain a printed matter with the same or similar color to the measured object. For example, if the 125th color density is selected as the closest color density to the combination of color densities obtained by measuring the object to be measured, then from the table in Figure 2, the C version is 30%, and the M version is 0.
%, and the Y version is output as 10% by the dot area ratio output means.

By the way, depending on the combination of halftone area ratios output in this way, one part of them may be
It is well known that it can be replaced with Bk ink. Therefore, in the present invention, a human determines whether or not it can be replaced with Bk ink based on the contents of the combination of outputted dot area ratios, and then determines the dot area ratio of the Bk version by determining the dot area ratio of the Bk version. The rate calculation means 50 calculates the rate. Alternatively, conditions for replacing with Bk ink are set in advance, and when the conditions are met, the combination of halftone area ratios corresponding to the color information selected by the color information selection means 40 is outputted to the output means. Bk halftone area ratio calculation means 5 without outputting or with outputting
0, the halftone dot area ratio of the Bk plate can be determined.

Alternatively, the operator can visually check the color of the object to be measured.
You may decide in advance whether it is better to replace it with Bk ink. In this case, if it is determined in advance that a portion of each YMC ink is to be replaced with Bk ink, the one closest to the color information stored in the second storage device is selected. It is also possible to directly enter the processing by the Bk halftone dot area ratio calculation means without going through the steps.

It is desirable to be able to switch so that any one of these can be selected.

Based on the combination of halftone area ratios corresponding to the color information selected by the color information selection means 40
The following procedure may be used to determine whether or not to perform processing by the Bk halftone dot area ratio calculating means.

First, use Bk ink for brown and gray colors.
It is a good color to replace part of YMC's ink, and one criterion for judgment is whether it is such a color or not. So, for example, to judge whether it is brownish or not, the dot area ratio of CMY is 10 each.
It is possible to adopt criteria for whether or not the conditions of ~80%, 50% or more, or 50% or more are met.

For example, to judge it as gray, the difference between the maximum and minimum dot area ratio of CMY is required.
It is possible to adopt a condition of 20% or less.

Furthermore, in the case of dark colors that cannot be expressed with normal YMC three-color printing, Bk ink can be used to print CMY.
Sometimes it can be expressed successfully by replacing some of the three colors of ink.

For dark colors in such a case, for example, the halftone dot area ratio of the object to be measured is all 10% or more, and at least one of the colors is 100% (or 100% if interpolation processing is performed as described below). (It may be more than that). For example, if the color is dark blue, CM
The halftone area ratio of Y is 115%, 30%, and 10%, respectively. When actually printing this, set C to 100%
However, if you do this, the color balance will be disrupted. Therefore 115% of C
Normalize other colors to 100% and convert CMY
When printing with the respective halftone area ratios of 100%, 26%, and 9%, the colors end up lacking in depth compared to the color of the object to be measured.

For such colors, CMY is used depending on the Bk version.
By replacing part of the ink, you can obtain the same color and satisfactory density. Therefore, the criteria for determining whether it is better to replace such a dark color with Bk ink is, for example, if the dot area ratio of CMY is all 10% or more,
It is sufficient to set a condition that at least one color is 100% (or more than 100%).

Whether or not the above conditions are met can be determined automatically as described above, or it can be determined manually based on the results output by the halftone area ratio output means. Either is fine.

Next, processing by the Bk halftone dot area ratio calculating means will be explained.

First, as an initial setting condition, what percentage
You must decide whether to include the Bk version.

The Bk plate is originally used to compensate for the lack of density in the shadow areas, so it only needs to be used from the middle to the shadow areas. This is called a skeleton black. However, according to the theory of color reproduction, various formats can be used for Bk plates, starting from skeleton black to full black, which uses as much Bk plate as possible with three-color plates as much as possible. There are many combinations in which the printed results can be made exactly the same by appropriately changing the amount of three-color plates depending on the format. FIG. 6 shows skeleton black and full black tone reproduction curves, and various types of intermediate black curves can be taken between them. Figure 7 is an explanatory diagram of the format of the Bk plate, and when the format of the Bk plate is changed to reproduce a certain brown color as shown in Figure 7 Aa, what combination of three-color plates is used? It shows you what to do. If you use skeleton black as shown in Figure 7 AB, the Bk version will not be used at all, but if you use full black as shown in Figure 7 AC, the density of the C version, which is the version with the lowest density, will be replaced with the Bk version. There is.

Further, FIG. 7 Ad shows an example in the case of intermediate black. Figure 7B is an explanatory diagram of another example of the Bk version format, and the black color shown in Figure 7Ba is shown in Figure 7B.
Bb shows the case where the skeleton black Bk version is used, and Figures 7Bc and 7Bd show the cases where the full black and intermediate black Bk versions are used, respectively.

It is necessary to decide in advance which format to use among these various Bk version formats. Based on the determined Bk plate format, the halftone area ratio of the Bk plate and the three-color plate is determined.

Next, a search is made to find out which of the densities corresponding to the CMY version measured through the RGB filter has the lowest value. Looking at the brown example in Fig. 7 Aa in Fig. 7, the C concentration is the lowest value. How much of this concentration is to be replaced with the Bk version is determined by
Determined by version format. Bk for full black
The entire C plate density is replaced by the plate, and if it is an intermediate black or skeleton black, the C plate density is replaced by a Bk plate which changes variously depending on the conditions described above.
Let B _R be the density of the C plate to be replaced with this Bk plate.

Next, the required dot area ratio of the Bk plate using the Bk plate calculation data stored in the first storage means is determined. Examples of the data for calculation of the blackout plate are shown in FIGS. 3 and 4. In FIG. 4, the horizontal axis is the Bk dot area ratio, and the vertical axis is the density measured through the RGB filters. Find the intersection of the density B _R replaced by the Bk version obtained above and the density measured via the R filter,
By reading the value on the horizontal axis at that point, the dot area ratio of the Bk plate can be determined. This was decided
M that is replaced with the Bk version by reading the density through the BG filter in the dot area ratio of the Bk version
The densities B _G and B _B of the plate and Y plate are found.

Next, calculate the density values of the remaining versions that are not replaced with the Bk version.The density values that are not replaced with the Bk version are D _1R , D _1G , for the density through each RGB filter.
D _1B is calculated using the following formula.

D′ _R = D _R −B _R D′ _G = D _G −B _G D′ _B = D _{B −B} Note that D _R , D _G , and D _B are the concentrations of the object to be measured through the RGB filter, and B _R , B _G , B _B are the respective densities to be replaced with the Bk version. D′ _R , D′ _G , and D′ _B are color information in consideration of the Bk version when color density is adopted as color information.

The same thing can be done when using chromaticity or other information other than color density as color information.

Using the color information considering the Bk version obtained as described above, the color information selection means selects the Bk version.
The color information closest to the color information considering the plate is selected from the color information-dot area ratio conversion table.

The combination of dot area ratios corresponding to the color information thus selected and the dot area ratio of the Bk plate are outputted by the dot area ratio output means 60.

Note that the color information closest to the color information stored in the second storage means is selected from the color information to halftone dot area ratio conversion table, and the Bk version is created according to the result of calculating the corresponding halftone dot area ratio. In some cases, a combination of halftone area ratios taken into account may be obtained, and in such a case, the color information selection means replaces the color information stored in the second storage means with color information that takes the Bk version into account. All you have to do is process it.

As the dot area ratio output means, a display device such as a printer, a display tube, or a CRT display can be used. Further, in order to input the determined dot area ratio to an external device such as a layout scanner, it may be outputted to a data storage medium such as a floppy disk, magnetic tape, or paper tape, or it may be directly outputted to an external device. It's okay.

However, the accuracy of the halftone dot area ratio determined as described above depends on the accuracy with which the halftone dot area ratio in the color information to halftone dot area ratio conversion table is created. In the example shown in FIG. 2, the dot area ratio is changed at 10% intervals, so the accuracy is up to 10%.

Therefore, if a more accurate halftone area ratio is required, it is sufficient to create a color information to halftone area ratio conversion table with the required accuracy.
In this case, the amount of data in the color information/halftone dot area ratio conversion table becomes extremely large, and creating such data not only requires a great deal of time and effort, but also requires a storage device with a large storage capacity. This method has the disadvantage that it takes a long time to perform comparison calculations with measurement data of the object to be measured.

In the following, interpolation for eliminating such drawbacks and determining the halftone dot area ratio at intervals finer than the data interval of the halftone dot area ratio in the color information/halftone dot area ratio conversion table will be explained.

First, the color information selected by the color information selection means 40 as described above is selected when the distance SA=0, that is, it is selected as a result of completely matching the color information of the object to be measured or the color information considering the Bk plate. In this case, the corresponding combination of dot area ratios may be output as is by the dot area ratio output means 60. However, if the selected color information is
If it is selected in a case other than SA=0, the halftone area ratio corresponding to the selected color information is interpolated, and the halftone dot area ratio corresponding to the selected color information is interpolated to print a color that is even closer to the color of the object to be measured. Output the combination of point area ratio. The interpolation of the dot area ratio may be performed by any suitable method, and a dot area ratio interpolation means for this purpose may be provided as desired.

How to interpolate the dot area ratio will be described below based on embodiments.

First, from the color information to halftone dot area ratio conversion table with halftone dot area ratios in 10% intervals as shown in Figure 2, the one closest to the color density combination d (D _R , D _G , D _B ) of the object to be measured is selected. is selected, and the combination of color information is t(T _R ,
T _G , T _B ) and the corresponding combination of halftone area ratios is P (c, m, y). In this case, for example, it is assumed that it is desired to obtain even a dot area ratio of the order of 1%. In this case, the halftone area ratio to be found is P
Half of 10%, or 5, is the dot area ratio centered on
% in the direction of magnitude.

Figure 8 shows A (c
+5, m-5, y+5), B(c+5, m+5, y
+5), C(c+5, m+5, y-5), D(c+
5, m-5, y-5), E(c-5, m-5, y+
5), F (c-5, m+5, y+5), G (c-5,
m+5, y-5), H(c-5, m-5, y-5),
, and the desired halftone area ratio exists in a solid whose vertices are these points.

Therefore, divide this solid into parts with the required precision as shown in Figure 8, and calculate the combination of color densities for each combination of halftone area ratios shown by each grid point, and use the above-mentioned formula to calculate the distance of color densities. It is sufficient to select the point where the distance is the minimum and determine the combination of dot area ratios at that point as a combination of dot area ratios with increased accuracy.

However, the above A, B, C, D, E, F, G, H
The dot area ratio of the point is known as mentioned above,
The corresponding color density is unknown.

Therefore, A'(c+10, m-
10, y+10), B'(c+10, m+10, y+10),
C' (c+10, m+10, y-10), D' (c+10, m-
10, y-10), E'(c-10, m-10, y+10),
F'(c-10, m+10, y+10), G'(c-10, m+
10, y-10), H'(c-10, m-10, y-10) and their respective midpoints I(c, m-10, y+10), J
(c, m+10, y+10), K(c, m+10, y-
10), L(c, m-10, y-10), M(c+10, m,
y+10), N(c+10, m+10,y), O(c+10,
m, y-10), Q(c+10, m-10, y), R(c,
m, y+10), S(c, m+10, y), T(c, m,
y-10), U (c, m-10, y), V (c-10, m,
y+10), W(c-10, m+10, y), X(c-10,
m, y-10), Y(c-10, m-10, y), Z(c+
Since the combination of color densities of ZZ (c-10, m, y) and ZZ (c-10, m, y) can be found from the color density-dot area ratio conversion table, first, the color density of each of these points and the point P Using the color density values of A, B,
The combination of color densities of points C, D, E, F, G, and H is determined by interpolation calculation.

FIG. 9 shows the position of each point 10% away from point P in the C, M, Y coordinate system representing the halftone area ratio. First, a method for determining the combination of color densities at point A (c+5, m-5, y+5) using an interpolation method will be described. Point A is A′(c+10,
m-10, y+10), M(c+10, m, y+10), Z
(c+10, m, y), Q (c+10, m-10, y), I
(c, m-10, y+10), R (c, m, y+10), P
(c, m, y) and U (c, m-10, y). Therefore, point A′,
The average of each color density component of M, Z, Q, I, R, P, and U is determined, and the value is taken as the color density component of point A, that is, the combination of the color density of point A.

Note that if the color density/dot area ratio conversion table is not created using equally spaced dot area ratios, a solid consisting of points A', M, Z, Q, I, R, P, and U will be used. may be a rectangular parallelepiped rather than a cube, and in that case, the distance of point A from each vertex of the rectangular parallelepiped will be different, so use a proportional calculation formula or an appropriate function depending on the distance from each vertex. All you have to do is ask for it.

Similarly, other points B, C, D, E, F, G, H
Also calculate the combination of color densities for each of them.

As above, points A, B, C, D, E, F,
Now that we have found the combinations of color densities for all of G and H, we can use the color densities at these points to determine the colors of each lattice that divides the cube at required intervals as shown in Figure 8. Combinations of concentrations are determined by an appropriate method such as proportional allocation in the same manner as described above. Next, the combination of the color densities of each grid point obtained in this way and the color densities of the object to be measured d(D _R , D _G ) D _B )
Select the grid point that minimizes the distance SA between. Since the combination of dot area ratios at the grid points selected in this way is already known,
The combination of the dot area ratios is output from the dot area ratio output means 60 as data obtained by interpolating the combination P (c, m, y) of the dot area ratios of the object to be measured.

By the way, points A, B, C, as shown in FIG.
Obtaining the combination of color densities at all the grid points with the required precision for all areas D, E, F, G, and H requires a large number of grid points, making the processing difficult. Therefore, consider eight small solid bodies whose diagonal lines are the lines connecting point P and each vertex in FIG. In this way, the desired combination of color densities will be included in one of these small solids. Where it is included is determined by the combination of color densities of the object to be measured d (D _R , D _G , D _B )
is determined based on which point is closest to the combination of color densities of vertices A to H.

Once a small solid is determined in this way, the combination of color densities of each lattice point separated by the required precision is determined by interpolation only for this small solid, and then the combination of color densities of each lattice point in this small solid is determined by interpolation. The grid point closest to the combination d (D _R , D _G , D _B ) of the color densities of the object to be measured may be selected from among them. In this way, the calculation time can be reduced to about one-eighth.

When the color information in the color information-dot area ratio conversion table and the color information of the object to be measured completely match, the dot area ratio output means 60 outputs the dot area ratio corresponding to the matched color information. If they do not match completely, a combination of halftone area ratios interpolated as described above is output.

Note that the required halftone area ratio may be input using a numeric keypad or the like.

FIG. 10 is an explanatory diagram of another interpolation method.
The G and B axes represent the color densities obtained through the R, G, and B filters, respectively, and the color density combination t(T _R ,
T _G , T _B ) is the origin.

Here, if the vector B→td (B _R , _BG , _BB ) is set, _BR = _DR − T _R , _BG = _DG − T _G , and _BB = DB − _{T B.}

Further, the dot area ratio is shifted by 1 unit (i.e., 10% in the case of FIG. 2) for the combination P (c, m, y) of the dot area ratio corresponding to the color density combination t. combination P ₃ (c±10, m±10, y
±10) and the corresponding color density combination
t ₃ (T _R3 , T _G3 , T _B3 ) can be found from the color density to halftone dot area ratio conversion table.

The dot area ratio P ₃ (c±10, m±10, y±10)
Whether to take a positive or negative value is determined depending on whether each component of the vector B → td (B _R , B _G , B _B ) is greater than or equal to zero or less than zero, and if it is greater than or equal to zero, then It is taken as a positive value, and if it is smaller than zero, it is taken as a negative value. In this case, the numbers to be adopted for each of c±10, m±10, and y±10 are determined by the numbers B _R , B _G , and B _B .

In this way, color information data near the color information selected by the color information selection means is obtained from the color information to halftone dot area ratio conversion table. Color information data in this vicinity can be obtained from that number.

Here, considering vector B → tt ₃ , vector B → tt ₃
can be expressed as a composition of several vectors.

For the sake of simplicity, the following explanation will be based on the case where each component of the vector Btd is greater than zero, but the same procedure can be performed even in other cases.

The combinations of dot area ratios when the c component increases by 10% and when the c component and m component each increase by 10% with respect to the above combination of dot area ratios P (c, m, y) are respectively P ₁ (c+10, m, y),
P ₂ (c+10, m+10, y) The color density combinations corresponding to the above-mentioned halftone dot area ratio combinations P ₁ and P ₂ are respectively t ₁ (T _R1 , T _G1 , T _B1 ) and t ₂ (T _R2 ,
T _G2 , T _B2 ).

Therefore, vector B→tt ₃ is vector B→tt ₁ , B→t ₁ t ₂
，
By B→t ₂ t ₃ , B→tt ₁ +B→t ₁ t ₂ +B→t ₂ t ₃ =B→t
It can be expressed as _t3 .

Therefore, vector B→td is vector B→tt ₁ , B→t ₁ t ₂
，
By B→t ₂ t ₃ , αBtt ₁ + βB→t ₁ t ₂ , ₁ B→γt ₂ t ₃ =
It can be expressed as B → td.

Here, each component of the vector B→td (B _R , B _G , B _B ) is known as described above, so from the above relational expression α,
Find β.

Therefore, the color density combination d(D _R , D _G ,
The combination of halftone area ratios P( _c ,
The combination of dot area ratios P′(c′,
m', y') are at 10% intervals in the table in Figure 2, so c' = c + α x 10 m' = m + β x 10 y' = y + γ x 10.

As described above, the combination of halftone area ratios after interpolation
P′(c′, m′y′) is determined.

Note that there are various methods of expressing the vector B→tt ₃ as a combination of other vectors in addition to the above, and any vector may be used.

However, in order to obtain a reasonable interpolated value, the first step is to
It is preferable to select vectors such that the vector obtained by connecting the combinations of color densities obtained from the color density-dot area ratio conversion table reaches the color density combination _t3 , as shown in FIG.

If the vector method is adopted in this way, the processing time required for interpolation to find the combination of highly accurate halftone area ratios can be extremely shortened.

Furthermore, the interpolation of the dot area ratio can be performed in the same manner not only for color density but also for chromaticity.

FIGS. 11 and 12 are flowcharts showing how the halftone area ratio is determined in the present invention, and FIG. This is a case where it is decided whether or not a Bk version is necessary based on the result of the halftone area ratio corresponding to the color information that is closest to the color information stored in the device. This shows what happens when you have already decided that you need .

Since the present invention has the above configuration, it has the following effects.

First of all, according to the device of the invention of this application:
Even if the colors to be reproduced in printing are specified as actual colors, such as in a color sample, it is extremely easy and quick for even non-experienced users to determine the colors of each color to reproduce the specified colors. The dot area ratio of the halftone positive can be determined.

Next, according to the device of the invention of this application, the halftone positive halftone dot area ratio of each plate is always determined in a standardized form, unlike the conventional method in which humans judge it, so the quality of printed matter can be controlled. becomes easier.

Further, according to the invention of this application, in addition to the above-mentioned effects, by further employing an interpolation means, it is possible to determine the halftone area ratio with the necessary accuracy extremely easily.

In addition, as a color sample, colors that do not require a Bk plate are often used, but even in cases where a Bk plate is required, the present invention makes it possible to determine the halftone area ratio in consideration of the Bk plate. can. In this case, according to the present invention, there is no need for a color density/tone dot area ratio conversion table that combines the four versions of Y, M, C, and Bk by changing the dot area ratios with a predetermined precision. Only the color density/halftone dot area ratio conversion table for the three colors M and C and the data for calculating the Bk plate are required, so that the storage capacity can be saved and the calculation time can also be shortened.

[Brief explanation of drawings]

Figure 1 is a conceptual diagram of the device of this invention, Figure 2 a,
b is an explanatory diagram of a color density-dot area ratio conversion table;
Fig. 3 is a table as an example of data for Bk plate calculation, Fig. 4 is a graph by a function as an example of data for Bk plate calculation, Fig. 5 is a graphic diagram of one embodiment of the color measuring means, and Fig. Figure 6 is a skeleton black and full black tone reproduction curve, Figures 7A and 7B are explanatory diagrams of the Bk version format for brown and black colors, respectively, and Figures 8, 9, and 10 are mesh reproduction curves. Diagram for explaining the method of interpolation processing of point area ratio,
FIGS. 11 and 12 each show a flowchart of an example of determining a combination of dot area ratios using the apparatus of the present invention. 1...Object to be measured, 10...First storage means, 2
0...Color density measuring means, 21...Light source, 22...
Filter, 23... Photoelectric conversion element, 24... Amplifier, 25... Correction circuit, 26... Logarithmic converter,
27... A/D converter, 28... Display meter, 30... Second storage means, 40... Color density selection means, 50... Bk halftone area ratio calculation means,
60...Dot area ratio output means.

Claims (1)

[Scope of Claims] 1. A color information-dot area ratio conversion table showing the correspondence between color information and a combination of dot area ratios corresponding to the color information of color separation plates of three colors Y, M, and C. and Bk
The first one stores Bk plate calculation data indicating the correspondence between the halftone area ratio of the color separation plate and the color information.
a storage means, a color measurement means for measuring the color of the object to be measured to obtain color information, and a second storage means for storing the color information obtained by the color measurement means;
Based on preset conditions, calculate the halftone dot area ratio of the Bk plate from the color information stored in the second storage means and the Bk plate calculation data stored in the first storage means, and calculate the dot area ratio of the Bk plate. Bk dot area ratio calculation means for subtracting color information corresponding to the Bk dot area ratio from the color information stored in the second storage means to obtain color information taking the Bk version into consideration;
The color information-dot area ratio conversion table stored in the first storage means is compared with the color information stored in the second storage means and/or the color information considering the Bk plate, and the color information selection means for selecting the color information stored in the second storage means and/or the color information in consideration of the Bk plate from among the color information in the color information-dot area ratio conversion table; , a halftone dot area ratio output means for outputting a combination of halftone dot area ratios corresponding to the color information selected by the color information selection means and a halftone dot area ratio of the Bk plate. Area ratio determination device. 2. The combination of halftone area ratios corresponding to the color information selected by the color information selection means is based on the color information -
2. The dot area ratio determination device according to claim 1, wherein the interpolation process is performed by an interpolation means that performs interpolation processing based on a dot area ratio conversion table.