JP4803010B2 - 2-color printing data creation method - Google Patents

Description

  The present invention relates to a two-color print data creation method for creating data for two-color printing.

Conventionally, printing with two-color ink has been performed on a folded flyer or the like. In these printings, printed matter is created with two colors of ink, and images and characters are reproduced in two colors.
As a method for creating these printing data, there is a method in which four colors of print data are created as in normal printing, and data corresponding to the ink used for two-color printing is used (see Patent Document 1).
JP 2000-101856 A

However, in the method of printing by using the data corresponding to the ink for two colors out of the four color data of normal printing, there is a lack of plate data that is not used for printing, and the gradation of those plates is not reproduced. Therefore, the data is not suitable for two-color printing, and some correction is necessary.
In addition, in this correction, it is difficult to imagine what colors the two colors will be reproduced, and it takes considerable skill to perform these correction operations, and a great amount of work load and work is required. I need time.
Furthermore, when creating data for two-color printing directly from a natural image, special conditions must be set in the color separation process using a scanner or the like, and the operator can choose what color the two colors are reproduced. It is difficult to determine whether or not it is necessary to perform these operations, and there is a problem that a great work load and work time are required.

  The present invention has been made in view of the problems of the prior art described above, and the object of the present invention is not to impair gradation, and does not require skill, and can be performed simply or automatically. An object of the present invention is to provide a two-color printing data creation method for creating two-color printing data from four-color printing data with a short work time.

  In addition, it does not impair the gradation of natural images, and does not require special conditions or skill, so it can be used for simple operations or automatically, with a short work time, and for direct two-color printing from natural images. An object of the present invention is to provide a two-color printing data creation method for creating data.

In order to achieve the above object, a two-color printing data creation method according to the present invention is a two-color printing data creation method for creating data for two-color printing printed by cyan and magenta. ) Determining the darkest color to reproduce according to the characteristics of the input image data;
(B) obtaining the darkest color reproduced by two-color printing according to the characteristics of two-color printing; and (c) input data from the darkest color of these input image data and the darkest color of two-color printing. A step of determining a lightness conversion function that linearly converts the lightness of the darkest color of the image into the darkest lightness of two-color printing; and (d) a step of converting the input image data into a colorimetric value and further converting it into a CIELAB coordinate value. (E) converting CIELAB L * obtained in steps (e) to L * ′ for two-color printing in accordance with the lightness conversion function, and (e) CIELAB obtained in steps (f) and wherein the a * within the range of colors of the two-color printing that includes the steps of searching for a color to reproduce L * 'obtained in (e) from 2-color printing color among the coordinate values .

Further, the two-color printing data creation method according to the present invention is a two-color print data creation method for creating two-color print data printed with two colors of ink, and (g) according to the characteristics of the input image data, A step for obtaining the darkest color, (g) a step for obtaining the darkest color reproduced by two-color printing according to the characteristics of two-color printing, and (g) the darkest color and two colors of these input image data A step of determining a lightness conversion function that linearly converts the lightest color of the input data to the darkest lightness of the two-color print from the darkest color of the print, and (e) out of the two colors according to the characteristics of the two-color print The CIELAB value reproduced with the maximum amount of one color is obtained, the CIELAB value reproduced with the maximum amount of the remaining one color is obtained, the line segment connecting those coordinates is obtained, and the input image data is measured. Converted to a value Line orthogonal and converting the coordinate values of CIELAB, the line segment obtained in (k) in accordance with brightness conversion function obtained at step CIELAB of L * obtained in step (co) (Ke) (co) The color value L * ′ in the upper part and the CIELAB a * and b * color coordinates obtained in steps (i) and (co) are orthogonal to the line segment obtained in (co) and A step of obtaining a plane including a line segment passing through the CIELAB coordinates and parallel to the L * axis; and (2) the color obtained by the step ( 2) and the color gamut of two-color printing intersect, and the color of two-color printing And a step of searching for a reproduction color of the two-color printing that reproduces a color of the two-color printing that becomes L * ′ within the range .

Further, the two-color printing data creation method according to the present invention is a two-color print data creation method for creating two-color print data to be printed with two colors of ink. Determining the darkest color to be reproduced; (c) determining the darkest color reproduced by two-color printing according to the characteristics of two-color printing; and (e) the darkest color and two colors of these input image data. The two-color printing obtained in the steps of (b) and (c), and the step of determining a lightness conversion function that linearly converts the lightest color of the input data from the darkest color of the print to the darkest lightness of the two-color print A step of obtaining a line segment connecting the darkest color reproduced in CIELAB and the origin of CIELAB or paper white, (h) converting input image data into colorimetric values, and further converting into CIELAB coordinate values; (Tu) A step of converting L * of CIELAB obtained in step (h) into L * ′ according to the lightness conversion function obtained in step (so); a * of CIELAB obtained in step (t) (h); a step of obtaining a plane parallel to the L * axis, passing through the CIELAB coordinates of the original image, in parallel with the line segment obtained from (b) from the b * color coordinates ; And a step of searching for a reproduction color of two-color printing that intersects with the color gamut of two-color printing and reproduces a color of two-color printing that is L * ′ within the range of the color of two-color printing. To do.

By using the present invention, high-quality two-color printing data can be created from four-color printing data easily and without any time and skill, and without any lack of tone. In addition, high-quality two-color printing data can be created from a color image easily and without time and skill, and without any lack of tone.
In addition, when two-color printing data is created from a natural image, it is suitable for creating two-color printing data because it reproduces two-color printing that is optimal not only by hand but also perceptually.
In addition, when converting from four-color printing data to two-color printing data, two-color printing that is optimally perceptually and manually is reproduced. It is suitable for converting to 2-color print data.

Hereinafter, an embodiment of the two-color printing data creation method of the present invention will be described.
1, 2 and 3 are functional block diagrams for realizing the two-color printing data creation method according to the embodiment of the present invention. 2 and 3, the same or corresponding parts as those in FIG. 1 are denoted by the same reference numerals.
The two-color printing data creation method according to the present embodiment is a two-color printing data creation method for creating data for two-color printing printed by cyan and magenta. As shown in FIG. A function 1 for obtaining the CIELAB value that is the darkest color to be reproduced according to the characteristics of the data, a function 2 for obtaining the CIELAB value that is the darkest color to be reproduced by the two-color printing according to the characteristics of the two-color printing, and these inputs A function 3 for defining a lightness conversion function for linearly converting the darkest lightness of the input data to the darkest lightness of the two-color printing from the darkest L * value of the image data and the darkest L * value of the two-color printing; A conversion function 4 that converts input image data into colorimetric values, and further converts them into CIELAB coordinate values; and CIELAB L * obtained by the conversion function 4 is converted into L * ′ according to the lightness conversion function. This is realized by a conversion function 5 and a function 6 for searching a color that reproduces a * and L * ′ obtained by the lightness conversion function 5 among the CIELAB coordinate values obtained by the conversion function 4 from two-color printing colors. The

  Also, a two-color print data creation method for creating two-color print data to be printed with two color inks, as shown in FIG. 2, the CIELAB value that is the darkest color to reproduce according to the characteristics of the input image data According to the characteristics of the two-color printing, the function 2 for determining the CIELAB value that is the darkest color reproduced by the two-color printing, the darkest L * value of these input image data, and the most of the two-color printing One of the two colors according to function 3 for determining a lightness conversion function that linearly converts the lightness of the darkest color of the input data from the dark L * value to the darkest lightness of two-color printing, and the characteristics of two-color printing The CIELAB value reproduced with the maximum amount of CIELAB is obtained, the CIELAB value reproduced with the maximum amount of the remaining one color is obtained, the line segment connecting those coordinates is obtained, and the input image data is converted into the colorimetric value. And CI A conversion function 15 for converting the coordinates into LAB coordinate values; a function 16 for converting CIELAB L * obtained by the conversion function 15 into L * ′ according to the lightness conversion function; and a CIELAB a * obtained by the conversion function 15 , B * is on the line segment orthogonal to the line segment from the color coordinates, and is realized by the function 17 for searching for the reproduction color of the two-color printing that reproduces the color of the two-color printing of L * ′.

  Also, a two-color print data creation method for creating two-color print data printed with two colors of ink, as shown in FIG. 3, a CIELAB value that is the darkest color to be reproduced according to the characteristics of input image data According to the characteristics of the two-color printing, the function 2 for determining the CIELAB value that is the darkest color reproduced by the two-color printing, the darkest L * value of these input image data, and the most of the two-color printing A function 3 for determining a lightness conversion function for linearly converting the lightness of the darkest color of the input data to the darkest lightness of two-color printing from the dark L * value, and a function for obtaining the darkest color reproduced by the two-color printing 2 for obtaining a line segment connecting the darkest color reproduced by two-color printing obtained in 2 and the origin of CILELAB, and conversion for converting input image data into colorimetric values and further converting into CIELAB coordinate values Function 4, a lightness conversion function 5 for converting CIELAB L * obtained by the conversion function 4 for converting to CIELAB coordinate values into L * 'according to the lightness conversion function, and a conversion function for converting the CIELAB coordinate values to CIELAB coordinate values In the two-color printing of L * ', which is on a line segment parallel to the line segment obtained by the function 18 for obtaining the line segment connecting the origins of CILELAB from the CIELAB a * and b * color coordinates obtained in 4 This is realized by the function 19 for searching for reproduction colors of two-color printing for reproducing colors.

FIG. 4 is an example in which colors reproduced by four-color printing are projected onto the a * -b * plane of the CIELAB space. FIG. 5 shows an example in which colors reproduced by two-color printing are projected on the a * -b * plane of the CIELAB space. Thus, in order to reproduce four-color printing by two-color printing, the color space of the four-color printing must be converted with respect to the two-color printing surface.
The conversion method for this purpose is shown below. Conversion is performed separately for the lightness direction conversion and the chromaticity direction.
In the lightness conversion method, the maximum lightness reproduced by four-color printing is Lo, max, the minimum lightness is Lo, min, the maximum lightness reproduced by two-color printing is Lr, max, and the minimum lightness is Lr. , Min, the lightness Lo for four-color printing is set as the lightness Lr for two-color printing according to the following relational expression (Equation 1).

  FIG. 6 shows one of the rules for converting the chromaticity direction. FIG. 6 is a diagram showing a method of mapping from four-color printing color to two-color printing color in the two-color printing data creation method according to the embodiment of the present invention. A method for converting point A of the original image on CIELAB into two-color printing is shown. In this case, what is indicated by the plane of P0-P1-P3-P2 is a color gamut by two-color printing. The b * value of the original image is ignored, and only the a * value is reproduced by two-color printing. The color gamut by two-color printing is a surface, and the lightness Lr reproduced in accordance with the relational expression (Equation 1) is also determined, so that the reproduction color B in the two-color printing is uniquely determined and is reproduced by the two-color printing. Color.

  FIG. 7 shows another example. FIG. 7 is a diagram showing another example of a method for mapping from four-color printing color to two-color printing color in the two-color printing data creation method according to the embodiment of the present invention. A method of converting point C of the original image on CIELAB into two-color printing is shown. A line segment connecting the position P1 where the color is developed with the maximum amount of one color and the position P2 where the color is developed with the maximum amount of the other one color is created. A plane S1 that is orthogonal to this line segment, passes through the CIELAB coordinates of the original image, and is parallel to the L * axis is obtained, and this S1 and the color gamut by two-color printing intersect to obtain Lr in the relational expression (Equation 1). This is a conversion method in which the point D is a reproduction color for two-color printing.

  FIG. 8 shows another example. FIG. 8 is a diagram showing another example of a method for mapping from four-color printing colors to two-color printing colors in the two-color printing data creation method according to the embodiment of the present invention. A method of converting the point E of the original image on CIELAB into two-color printing is shown. In two-color printing, a line segment connecting the position P3 where the two colors are developed to the maximum amount and nothing is developed, that is, the position P0 of the medium itself (or paper white) is created. A plane S2 parallel to the line segment and passing through the CIELAB coordinates of the original image and parallel to the L * axis is obtained, and further, this S2 and the color gamut by two-color printing intersect to obtain Lr in the relational expression (Equation 1). This is a conversion method in which the point F is a reproduction color for two-color printing.

In this embodiment, an example of conversion from four-color printing to two-color printing is shown. However, instead of four-color printing, conversion is performed directly from RGB in digital camera RGB, CRT, LCD monitor, etc. to CIELAB coordinate values. Then, conversion to two-color printing may be performed.
In this embodiment, Lo, max, Lo, and min are obtained from four-color printing. However, such information may be obtained from RGB of a digital camera, RGB of a CRT, an LCD monitor, or the like.
Moreover, although the conversion method was shown in this Embodiment, you may describe and use these methods as an ICC profile in an internal table.
In this embodiment, CIELAB is used as the color space. However, another color system such as CIEUV may be used.
In this embodiment, the lightness to be converted is obtained first. However, the chromaticity may be obtained at the same time as the chromaticity or before the lightness.

It is a functional block diagram for realizing the two-color printing data creation method of one embodiment of the present invention. It is a functional block diagram for realizing the two-color printing data creation method of one embodiment of the present invention. It is a functional block diagram for realizing the two-color printing data creation method of one embodiment of the present invention. It is the figure which showed typically the example of the color gamut by 4 color printing. It is the figure which showed the example of the color gamut by 2 color printing typically. It is a figure which shows the mapping method from the color of 4-color printing to the color by 2-color printing in the data preparation method for 2-color printing of one embodiment of this invention. It is a figure which shows the other example of the mapping method from the color of 4-color printing to the color by 2-color printing in the data preparation method for 2-color printing of one embodiment of this invention. It is a figure which shows the other example of the mapping method from the color of 4-color printing to the color by 2-color printing in the data preparation method for 2-color printing of one embodiment of this invention.

  1, 2, 3, 6, 16, 17, 18, 19 ... function, 4, 15 ... conversion function, 5 ... lightness conversion function.

Claims (3)

A two-color print data creation method for creating data for two-color printing printed by cyan and magenta,
(A) obtaining the darkest reproduced color according to the characteristics of the input image data;
(A) obtaining the darkest color reproduced by two-color printing according to the characteristics of two-color printing;
(C) A step of determining a lightness conversion function for linearly converting the lightness of the darkest color of the input data to the darkest lightness of the two-color printing from the darkest color of the input image data and the darkest color of the two-color printing. When,
(D) converting the input image data into colorimetric values and further converting them into CIELAB coordinate values;
(E) converting CIELAB L * obtained in step (d) into L * ′ for two-color printing according to the lightness conversion function;
(F) Of the CIELAB coordinate values obtained in step (d), the color that reproduces a * within the color range of two-color printing and L * 'obtained in (e) is obtained from the color of two-color printing. Searching, and
A two-color print data creation method comprising: A two-color print data creation method for creating two-color print data printed with two colors of ink,
(G) determining the darkest color to reproduce according to the characteristics of the input image data;
(H) obtaining the darkest color reproduced by two-color printing according to the characteristics of two-color printing;
(G) determining a brightness conversion function for linearly converting the brightness of the darkest color of the input data from the darkest color of the input image data and the darkest color of the two-color printing into the darkest brightness of the two-color printing; ,
(E) In accordance with the characteristics of two-color printing, obtain the CIELAB value that is reproduced with the maximum amount of one of the two colors, further obtain the CIELAB value that is reproduced with the maximum amount of the remaining one color, and determine their coordinates. Obtaining a connecting line segment, converting input image data into a colorimetric value, and further converting it into a CIELAB coordinate value;
(C) The CIELAB L * obtained in step (C) is converted to the color value L * ′ on the line segment orthogonal to the line segment obtained in (C) according to the lightness conversion function obtained in step (K). Converting, and
( H ) A line segment that is orthogonal to the line segment obtained in step (c) from the CIELAB a * and b * color coordinates obtained in step (co) and that passes through the CIELAB coordinates of the original image is parallel to the L * axis. Determining a plane;
(2) The plane obtained in step ( 2) intersects with the color gamut of two-color printing, and the two-color printing that reproduces the two-color printing color that is L * ′ within the two-color printing color range . Searching for reproduction colors;
A two-color print data creation method comprising: A two-color print data creation method for creating two-color print data printed with two colors of ink,
(S) According to the characteristics of the input image data, obtaining the darkest color to be reproduced;
(C) obtaining the darkest color reproduced by two-color printing according to the characteristics of two-color printing;
(E) a step of determining a lightness conversion function for linearly converting the lightness of the darkest color of the input data to the darkest lightness of the two-color printing from the darkest color of the input image data and the darkest color of the two-color printing; ,
(D) obtaining a line segment connecting the darkest color reproduced in the two-color printing obtained in step (c) and the origin of CIELAB or paper white;
(H) converting input image data into colorimetric values and further converting them into CIELAB coordinate values;
(C) converting CIELAB L * obtained in step (h) to L * ′ according to the lightness conversion function obtained in step (so);
(T) Obtain a plane parallel to the L * axis through the CIELAB coordinates of the original image, parallel to the line segment obtained in (T) from the CIELAB a * and b * color coordinates obtained in steps (t) and (h). Steps,
(G) Reproduction of two-color printing in which the plane obtained in steps (t) and the color gamut of two-color printing intersect and reproduce the color of two-color printing that is L * ' within the color range of two-color printing Searching for colors;
A two-color print data creation method comprising:

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