JP2009012353A - Process printing method and printing data preparation device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a process printing method which enables the printing of a color reproduction region wider than by a conventional method with the most common four color offset printing machine using special feature ink. <P>SOLUTION: The color of four color special feature ink comprises Japanese ink, indigo blue, red and yellow. A pigment for use in four color special feature ink comprises C.I.Pig.Black 7 for Japanese ink, C.I.Pig.Blue 15:3 and C.I.Pig.Green 7 for indigo blue, C.I.Pig.Red 81 for red ink, and C.I.Pig.Yellow 12 for yellow ink. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a process printing method using four colors of special color inks and a print data creation apparatus.

  With the spread of image processing software in recent years, an increasing number of designers create image data using a PC (Personal Computer) and a display when designing product packages and the like. In that case, the designer displays the image data of the design on the display and visually recognizes it, and determines the color. Finally, image data expressing colors with RGB values is created. After creating the image data, the designer sends the image data to the printing company, and the printing company prints a desired material based on the image data.

  Here, in conventional printing, process printing using inks of four colors (CMYK: Cyan (indigo), Magenta (red), Yellow (yellow), blakK)) is generally used. Since the color range that can be expressed by RGB values (hereinafter referred to as color gamut) is wider than the color gamut that can be expressed by CMYK, the image data expressed by RGB values is expressed using CMYK ink. When printing (printing), the color reproduction range was narrowed. Here, ink is generally used in process printing and offset printing, and is widely used in various printing fields.

  At present, inks of colors (special colors) that require particularly saturation are individually created, and in addition to the above four colors, these special color inks are set in a printing machine for printing. The special color ink is a color that is added when it is difficult to reproduce the color of the original document by using only the normal four process colors, and is, for example, green or purple. However, in this method, it is necessary to change the special color ink when the image data to be printed changes. For this reason, the operator of the printing machine must remove the special color ink every time the image data changes, clean the printing machine, and set the special color ink for the next image data in the printing machine. There was a problem that it was expensive and productivity was poor.

Further, in general oxidation polymerization dry ink, six color printing inks using dyes already exist in the market (for example, Pantone (registered trademark) hexachrome), but this product is used. Requires a printing machine having a printing unit for six colors, and a printing machine having a four-color printing unit, which is most commonly used, has a problem that printing with six colors cannot be performed. Here, Patent Document 1 discloses a technique for performing printing in four colors.
JP-A-10-315630

  The present invention has been made in view of the above points, and is a process printing method and print data creation apparatus that use special color inks and can print in a wider color reproduction range than conventional ones using the most common four-color offset printing press. The purpose is to provide.

  In order to achieve the above object, the present invention is a process printing method using four special color inks, wherein the four special color inks are black, indigo, red, and yellow. As for the pigment used in the special color ink, black ink is C.I. I. Pig. Black 7 and indigo ink is C.I. I. Pig. Blue 15: 3 and C.I. I. Pig. Made of Green 7, red ink is C.I. I. Pig. Red 81, yellow ink is C.I. I. Pig. A process printing method characterized by comprising Yellow 12.

  According to the present invention, in the above-described process printing method, when the density of the yellow ink is gradually increased at predetermined ratios, the color measurement is performed at each density in the ab plane coordinates of the Lab color system. The line connecting the coordinates of the measured colorimetric values is closest to the straight line and extends to the outer coordinates. I. Pig. It is characterized by using a yellow 12 yellow ink pigment.

  According to the present invention, in the above-described process printing method, the image data is subjected to FM screening, and the printing portion data generated using the four colors of black, indigo, red, and yellow is a shadow data network. The corrected printing plate data is generated by multiplying the point density by a magnification of a preset value, and printing is performed using the corrected printing plate data.

Further, according to the present invention, in the above-described process printing method, the h * value in the L * C * h * color system of each of the four special color inks of black, indigo, red, and yellow is 231.78 for indigo ink. ° ± 10 °, red ink is 351.00 ° ± 10 °, and yellow ink is 91.29 ° ± 10 °.

  Further, according to the present invention, the colors of the four special color inks are black, indigo, red and yellow, and the pigment used in the four special color inks is C.I. I. Pig. Black 7 and indigo ink is C.I. I. Pig. Blue 15: 3 and C.I. I. Pig. Made of Green 7, red ink is C.I. I. Pig. Red 81, yellow ink is C.I. I. Pig. A printing data creation device used for process printing using four color special color inks composed of Yellow 12, and stores correspondence data representing correspondence between L * a * b * values and the four colors of ink Relationship information storage means; conversion means for converting image data input by a user into specific color space data expressed by a value in a predetermined color space; and specific color space data converted by the conversion means Color separation means for creating print data separated into data for each color of the four inks based on the correspondence relation data stored in the correspondence relation information storage means, and the print data created by the color separation means are separated And an output means for outputting data for each of the four ink colors.

  According to the present invention, in order to increase the saturation of the pigment used in the indigo ink, the conventional C.I. I. Pig Blue 15: 3, C.I. I. Pig Green 7 was added. Even if the high-saturation indigo ink is used, if the purple color is expressed using the conventional type of red ink, the purple saturation will drop, and therefore the more highly saturated red pigment C . I. Pig. Red 81 was adopted. As for yellow ink, C.I. is a pigment that does not become reddish as the concentration increases. I. Pig. Yellow 12 was adopted. As a result, it is possible to print a wider color reproduction range than before.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, a method for examining ink pigments will be described.
FIG. 1 is a table showing pigment names of conventional and process printing inks according to an embodiment of the present invention. Here, C. I. Pig. The notation of Black 7 etc. is C.I. I. This means the name given to identify the pigment, called (Color Index) Name, and is widely used in general. Also, Pig. Is an abbreviation for Pigment. The same C.I. I. Even for (Color Index) Name ink, the value measured by applying the ink for each ink manufacturing company that manufactures the ink is usually different.

 For example, lead white is represented as Pigment White 1, and ocher is represented as Pigment Yellow 43. I. Name corresponds to the chemical structure of the pigment.

  Here, in conventional process printing, as shown in FIG. 1, four colors of ink (CMYK: Cyan (cyan), Magenta (red), Yellow (yellow), blacK (black))) are used from conventional pigments. Created and used for printing. Here, in the order of printing normally performed in the conventional four-color process printing (black (K) → indigo (C) → red (M) → yellow (Y)), the color to be printed later does not hide the lower color. And increase transparency. For this reason, “yellow” is also called “transparent yellow”.

  Since the color reproduction range that can be expressed by process printing using the conventional four colors of ink is narrower than the color reproduction range expressed by RGB values, it is possible to reproduce the pigment for three colors other than black (yellow, red, and indigo). Selected. The pigment for ink was selected while visually confirming the printing result.

  First, in selecting the indigo pigment, the conventional C.I. I. Pig Red 15: 3, C.I. I. Pig Green 7 was added. This C.I. I. The reason for adding Pig Green 7 is to increase the color saturation.

FIG. 2 is a diagram showing the reproduction range of each color printed with indigo ink using different indigo pigments.
In this figure, it is calculated from the colorimetric value data of the color printed by gradually increasing the density of the indigo ink of the conventional product using the indigo pigment (CI Pig Blue 15: 3) at a predetermined ratio. Printed by gradually increasing the density of the indigo ink of a newly developed product using the a and b values and the indigo pigment (CI Pig Blue 15: 3 + CI Pig Green 7) at a predetermined ratio The a and b values calculated from the colorimetric value data of the obtained color and the density of the indigo ink of the test product (Test-1 to 3) using other indigo pigments are gradually increased by a predetermined ratio. The figure of the ab plane in the Lab color system which plotted the a and b value calculated from the colorimetric value data of the printed color is shown. As shown in this figure, C.I. I. Pig Red 15: 3 and C.I. I. It can be seen that indigo ink using indigo pigments combining two pigments of Pig Green 7 has the highest saturation. Therefore, C.I. I. Pig Red 15: 3 and C.I. I. The indigo pigment combining two pigments of Pig Green 7 was adopted.

  In addition, when the saturation of indigo ink is increased, purple color cannot be expressed sufficiently satisfactorily when using purple ink of the conventional type to express purple color, even if the highly saturated indigo ink is used. End up. Therefore, in the diagram of the ab plane of the Lab color system, it is necessary to increase the saturation of the red color in order to keep the purple saturation higher. Therefore, the pigment (CI Pig Red 57: 1) used for the conventional red ink was changed to a pigment (CI Pig Red 81) having a higher saturation of the red color.

  In the case of yellow ink pigments, C.I. I. Although (Color Index) Name is not changed, it is necessary to use a product in which the color does not change as much as possible depending on the applied concentration. In other words, yellow ink tends to become reddish gradually as the density is increased. The line connecting the coordinates of the colorimetric values measured at different densities in the ab plane coordinates of the Lab color system when the yellow ink density is gradually increased at a predetermined ratio is printed. Close to a straight line and extend to outer coordinates, C.I. I. Pig. Yellow 12 yellow ink pigment was adopted.

FIG. 3 is a diagram showing the reproduction range of each color printed with yellow ink using different yellow pigments.
In FIG. 3, the horizontal axis represents the a coordinate of the Lab color system, and the vertical axis represents the b coordinate of the Lab color system. In the yellow 1, yellow 2, and yellow 3 inks, the yellow 1 (using a pigment of yellow ink of CI Pig. Yellow 12) is the most linear Lab color system ab. It turns out that it goes to the outer side of a plane coordinate, and has extended to the outer side coordinate. That is, as shown in FIG. 3, the ink of yellow 1 (using a pigment of yellow ink of CI Pig. Yellow 12) was adopted.

FIG. 4 is a diagram showing a color reproduction area printed using four-color inks.
This figure shows the indigo ink only (C = Cyan), indigo ink + using each pigment (black, indigo, red, yellow) of the conventional product, newly developed product (improved product), and test products 1-3. Red ink (BV = Blue Violet), red ink only (M = Magenta), red ink + yellow ink (R = Red), yellow ink only (Y = Yellow), indigo ink + yellow ink (G = Green) 6 Colors are created, and the six colors are used to obtain calculated Lab values from the colorimetric values of the density up to the top “solid” by changing the density from 25 without ink to white solid, The a and b values corresponding to “solid” of each color are plotted on the ab plane.

Then, a four-color spot color process printing ink is prepared using the pigment of the newly developed product (improved product). At this time, the result of printing the prepared ink by solid printing is measured with a reflection densitometer that measures with a CMYK (total absorption) filter, and the measurement result is brought close to the recommended density value described below. The density here means an optical density D that represents the degree to which light is reflected from a substance. When the intensity of incident light is I ₀ and the intensity of reflected light is I, the value expressed by the following equation: It is.

D = log ₁₀ (I ₀ / I)

  The recommended density for each of the four special color inks is Status E, the density of black is 1.85 ± 0.1, the density of indigo is 1.85 ± 0.1, and the density of red is 1.70 ±. 0.1, and the yellow density is 1.80 ± 0.1.

Next, as described above, using the improved pigment, the four-color spot color ink prepared with reference to the above recommended density value is printed by solid printing, and the result is measured with a reflection densitometer. FIG. 5 shows an improvement in L *, which is calculated from the result of printing a four-color ink prepared with reference to the above-mentioned recommended density value using a solid color, and measuring the result with a reflection densitometer, using the improved pigment. It is a table | surface which shows the value of h * (unit: degree) calculated using the value of a *, b *, C *. Here, the values of L *, C *, and h * are L * C * in which the color is expressed by lightness (L *), saturation (distance from the coordinate center) (C *), and hue angle (h *). This is a value in the h * color system, and L * is represented by a value common to L * in the L * a * b * color system.

  By the way, since the L * value and the C * value are values indicating lightness and saturation, they are fluctuating values that need to be adjusted each time depending on the color of the image data to be printed. Further, the a * value and the b * value include a saturation element in addition to the hue. Therefore, in the production of four-color inks used for four-color spot color process printing, only the value of h * representing the hue is a universally meaningful value. As shown in FIG. 5, among the four color inks, the h * values of indigo, red, and yellow ink are particularly significant, indigo ink is 231.78 °, red ink is 351.00 °, and yellow ink. Was 91.29 °. The ink is prepared so that the h * value of the ink used for the four-color spot color process printing takes a value in a range of ± 10 ° from the above-described value shown in FIG.

  Note that the above-described recommended density value is a reference value for a target in the initial stage of ink creation, and the final ink density may not be within the range of the recommended density value.

  By the way, the printing process generally undergoes a plate making process, a printing plate process, a printing process, and the like. The plate making process means making a printing plate film or data. The printing plate process means creating a plate from printing plate data. The printing process means that a plate is set in a printing machine and printed. Hereinafter, a method of creating printing plate data in which the shade of each color in the image data is expressed by halftone dots for each color will be described. Here, as a typical method for creating printing plate data, AM (Amplitude Modulation) screening that expresses light and shade by the size of regularly arranged halftone dots, and the density of halftone dots of the same size are used. There is FM (Frequency Modulation) screening that expresses color shading by changing. FIG. 6A is a diagram illustrating a printing result using the AM screening technique. 5a is an enlarged view of the encircled portion of FIG. FIG. 6B is a diagram illustrating a printing result using the FM screening method. 5b is an enlarged view of the encircled portion in FIG. When multicolor printing is performed by this AM screening method, there is a problem that interference fringes (moire) due to overlapping of halftone dots occur. In order to avoid this, a case where printing is performed by FM screening will be described below.

  While the FM screen avoids the moire problem, when the same image is printed by the AM screening method and the FM screening method, there is a problem that a difference in human appearance occurs in a dark portion (hereinafter referred to as a shadow portion). is there. That is, there is a tendency that the darkness of the dark portion is insufficient. As can be seen from the comparison of the enlarged views 6a and 6b in FIGS. 6 (a) and 6 (b), the AM screening increases the ink film thickness and density because the halftone dot is larger. Responsible.

  FIG. 7 is a diagram showing the relationship between the dot density and the density for one color when the same image is printed using the AM screening and FM screening techniques. The encircled portion 1001 is the above-described shadow portion. From this figure, the AM screening is performed at a location where the density of the halftone dot area is around 75% (for example, in the range of 65% ± 5% to 90% ± 5%). It can be seen that the difference in concentration from the FM screening is significant. In order to reduce this difference in density, it has been corrected by multiplying the dot density of the data of the shadow portion 1001 among the six color printing plate data subjected to FM screening by a preset magnification. Create plate data. This magnification is determined by a prior experiment, and is, for example, about 1.07. The magnification is not limited to a fixed value, but may be a variable value that varies depending on the dot density. Thereby, the density difference between the result of the AM screening process and the result of the FM screening process can be reduced, and the difference in appearance can be reduced.

Next, the flow of data until the designer creates color-separated image data for four-color printing from RGB image data created using the PC and image processing software owned by the designer will be described. .
FIG. 8 is a diagram showing a data flow from creation of image data created by the designer to creation of color-separated image data for four-color printing. Reference numeral 100 denotes a PC (print data generation apparatus) that generates image data obtained by separating the image data 101 into the above-described four colors. The PC 100 is data indicating correspondence between RGB values and L * a * b * values. The RGB profile 102, the CMYK profile 103 which is data indicating the correspondence between the conventional CMYK values and the L * a * b * values, the four colors and the L * a * b * values of the improved product shown in FIG. Are stored in a storage unit (not shown). The control unit (not shown) of the PC 100 is installed with an existing image conversion program 110 (conversion unit, color separation unit) having a function of converting data according to the above three profiles. The PC 100 is connected to a scanner (not shown), and has an input unit such as a keyboard and a display unit such as a CRT.

  First, the designer installs existing image processing software in the PC 100 and creates the image data 101. At this time, the created image data is data expressed by RGB values. Note that the RGB value image data may be image data created by a digital camera or the like. The designer instructs the input unit to start the image conversion program in the PC 100. Next, when the PC 100 activates the image conversion program, the image conversion program 110 requests image data from the display unit. The designer visually recognizes this, selects the created image data 101 from the input unit, and inputs data indicating that it is RGB value data. Next, the image conversion program 110 creates an L * a * b * data file 105 obtained by converting the input image data into L * a * b * values using the RGB profile 102 described above.

  In addition, the design image etc. which the designer created on the paper surface may be taken in by the PC 100 from the scanner. In this case, when the scanner captures an image, the PC 100 creates image data expressed in CMYK or RGB. Here, it is assumed that the scanner has a function of performing color separation into CMYK or RGB. When the image is captured by the scanner, the image conversion program creates an L * a * b * data file from the CMYK image data of the read image using the CMYK profile 103 as described above.

  Thereafter, the image conversion program 110 creates image data 106 obtained by separating the L * a * b * data file into four colors based on the four-color profile 104 and the interpolation calculation. The four-color profile 104 is obtained by printing the color using the above-described four colors (improved product) shown in FIG. 1 and the CMYK value of the color and the colorimetric value (Lab) value measured by the colorimeter. This data stores a plurality of correspondence relationships. Then, for each color, FM screening processing is performed as described above, density correction is performed, and corrected printing plate data is created. The designer sends the corrected printing plate data for each color, the information on the four-color ink (pigment name) and the printing order information to the printing company, and the printing company performs the printing process accordingly. It is assumed that 4-color ink information and printing order information are registered as attached information of a 4-color profile.

  As a result, image data can be created and separated into four colors using image processing software or a conventional scanner that separates image data into four colors of CMYK, so four colors can be obtained without investing in new equipment. Printing plate data can be created.

  In addition, this makes it possible to temporarily convert to a data file represented by L * a * b * values regardless of the representation format (RGB values, CMYK values, etc.) of the image data that is the source of printing, and then the 4-color profile. Therefore, it is possible to construct a unified environment that can always reproduce the colors expressed by the user's equipment.

  In the above-described embodiment, the designer creates image data (or a design image read by a scanner) with a desired color, converts it into an L * a * b * data file, and then decomposes it into four colors. The designer may have a color sample or a library that can be reproduced with four color inks in advance, and select the color from the color sample to create image data. Thereby, color separation for four-color printing can be performed smoothly.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes a design and the like within the scope not departing from the gist of the present invention. In addition, all the features shown in the present embodiment are not essential for solving the problem.

  The above-described print data creation apparatus has a computer system inside. The process described above is stored in a computer-readable recording medium in the form of a program, and the above process is performed by the computer reading and executing this program. Here, the computer-readable recording medium means a magnetic disk, a magneto-optical disk, a CD-ROM, a DVD-ROM, a semiconductor memory, or the like. Alternatively, the computer program may be distributed to the computer via a communication line, and the computer that has received the distribution may execute the program.

  The program may be for realizing a part of the functions described above. Furthermore, what can implement | achieve the function mentioned above in combination with the program already recorded on the computer system, and what is called a difference file (difference program) may be sufficient.

It is a table | surface which shows the pigment name of the ink for process printing. It is a figure which shows the reproduction range of each color printed with the ink of the indigo using a different indigo pigment. It is a figure which shows the reproduction range of each color printed with the yellow ink using a different yellow pigment. It is a figure which shows the reproduction area of the color printed using 4 color ink. It is a table | surface which shows the value of h * of the result of having printed four-color ink by solid printing and measuring the result with the reflection densitometer. It is a figure which shows the printing result using the method of AM screening and FM screening. It is a figure which shows the relationship between the dot density and the density | concentration about 1 color when the same image is printed using the method of AM screening and FM screening. It is a figure which shows the data flow until it produces the image data by which color separation was carried out for 4 color printing.

Explanation of symbols

100 ... PC
DESCRIPTION OF SYMBOLS 101 ... Image data 102 ... RGB profile 103 ... CMYK profile 104 ... Four color profile 105 ... L * a * b * data file 106 ... Image data decomposed into four colors 110 ... Image conversion program

Claims (5)

A process printing method using four color inks,
The colors of the four special color inks are black, indigo, red, yellow,
The pigments used for the four color special color inks are:
Black ink is C.I. I. Pig. Consisting of Black 7,
Indigo ink is C.I. I. Pig. Blue 15: 3 and C.I. I. Pig. Consists of Green 7,
Red ink is C.I. I. Pig. Red 81,
Yellow ink is C.I. I. Pig. A process printing method comprising: Yellow 12. In the ab plane coordinates of the Lab color system, when the density of the yellow ink is gradually increased at predetermined ratios, the line connecting the coordinates of the colorimetric values measured at each density is the straightest line. Extending to the outer coordinates, close to C. I. Pig. The process printing method according to claim 1, wherein yellow 12 yellow ink pigment is used.   The image data is subjected to FM screening, and the halftone density of the shadow data among the printing plate data generated using the four colors of black, indigo, red, and yellow is multiplied by a preset magnification. The process printing method according to claim 1, wherein the corrected printing plate data is created and printing is performed using the corrected printing plate data. In the L * C * h * color system of each of the four special color inks of black, indigo, red, and yellow, the h * values of the three colors indigo, red, and yellow are:
Indigo ink is 231.78 ° ± 10 °,
Crimson ink is 351.00 ° ± 10 °,
The process printing method according to any one of claims 1 to 3, wherein the yellow ink is 91.29 ° ± 10 °. The colors of the four special color inks are black, indigo, red, yellow,
The pigments used for the four color special color inks are:
Black ink is C.I. I. Pig. Consisting of Black 7,
Indigo ink is C.I. I. Pig. Blue 15: 3 and C.I. I. Pig. Consists of Green 7,
Red ink is C.I. I. Pig. Red 81,
Yellow ink is C.I. I. Pig. A printing data creation device used for process printing using four special color inks made of Yellow 12,
Correspondence information storage means for storing correspondence data representing the correspondence between L * a * b * values and the four color inks;
Conversion means for converting image data input by the user into specific color space data represented by values in a predetermined color space;
Color separation means for creating print data obtained by separating the specific color space data converted by the conversion means into data for each color of the four inks based on the correspondence data stored in the correspondence information storage means; ,
An output means for outputting data for each of the four ink colors obtained by separating the print data created by the color separation means.

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