JP2000062253A - Method for forming special color printing profile, and apparatus for forming proof sheet of special color printing document - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an apparatus which forms a proof sheet by a color printer thereby checking a color tone of a special color print with the use of a process form system and a color management system. SOLUTION: The method for forming a special color printing profile to be used in converting colors by a color management system includes a process in which a color chart obtained by a combination of colors used in the special color printing among four colors, namely, cyan, magenta, yellow and black is output, a process in which a combination of an L* value, an a* value and a b* value representing each color of the color chart in a standard color space is measured for each color, a process in which a look-up table showing a correspondence of a combination of values of the cyan, magenta, yellow and black constituting each color and the combination of the L*value, a*value and b*value of each color is formed for each color of the color chart, and a process in which the look-up table is converted to a binary look-up table conforming to a form of the profile.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a proof (proof printing) for spot color printing, and more particularly to a technique for obtaining a color proof for spot color printing using a color printer.

[0002]

2. Description of the Related Art In recent years, with the spread of DTP (Desktop Publishing), the productivity and cost reduction of a plate making system using a personal computer have been remarkable. Image input scanners are also enriched with so-called auto-setup functions that automatically perform separation settings for each original, and are capable of unmanned color separation of a large number of originals. Also, DTP
Many digital color printers, which can be connected to the system to output color images easily, and color copiers, which can output image data, have become widespread.

All of these DTP systems, scanners, printers, etc. are produced on the premise of printing with four process ink colors (hereinafter referred to as "process printing"). On the other hand, newspaper leaflets and the like need to be manufactured at a low cost and in a short period of time, so there are cases in which printing is performed with two special colors or single color inks instead of the process four color inks (hereinafter This is called "special color printing".) Even when performing spot color printing, the process printing system is diverted as the equipment used for plate making.

However, it is necessary to devise a method for making a plate for spot color printing using a system for process printing. In particular, for the gradation image part, for the image (CMYK) decomposed for process printing, plate making
Although it is performed by the TP system, only the plates of color plates (for example, magenta (M) and cyan (C)) of colors close to the inks used for special color printing (for example, red (R) and green (G)) are printed, This is printed with R and G inks. This is due to the following three reasons.

First, since the number of colors that can be used by the DTP system is limited, such as four colors or black ink, the system cannot handle two colors of image data. . So, use 2
In addition to the data for the color plate, it is necessary to insert dummy data and handle it as an image of four process colors in a pseudo manner.

Further, although many scanners and the like for performing automatic set-up for process four-color printing have been developed, there is almost no function of the scanner for performing image separation for special color printing. It is possible to perform spot color separation by manual setup, but it requires a high degree of skill and time. Therefore, in order to manufacture a printed matter at a low price and in a short period of time, it is necessary to disassemble by auto setup even if four colors are not required.

Further, by utilizing the image database, 4
If the same data is used for both color printing and special color printing, the four-color image data is stored in the database rather than easily managing the four-color image data and the two-color image data separately. It is more convenient to use it for spot color printing as needed.

For these reasons, it is usual to use the DTP system for process printing also in plate making for spot color printing. At this time, a 4-color image is displayed on the screen display on the monitor of the DTP system. In this case, if one of the images separated into three or four colors for process printing is omitted, it is difficult to reproduce the gradation of the color including this color.
As described above, since the screen display remains in four colors, it is very difficult to estimate what kind of color will be reproduced when special color printing is performed. Therefore, also in spot color printing, it is common to create a proof and confirm image reproduction before printing with this machine, as in process printing.

FIG. 9 shows a schematic configuration of a conventional spot color print making apparatus, and FIG. 10 shows a spot color print making process using the same. As shown in FIG. 9, the conventional system acquires color data such as images and illustrations with the scanner 50,
Further, if necessary, the data already stored in the database 51 is read out, and the DTP system 52 performs layout and editing work. The print original thus created is output to a film by the image setter 53, a printing plate is made by the plate making device 54, and a proof print is made by the flatbed proofing machine 55. Ask the client etc. to confirm the completed proof, and if there are corrections and changes, scan the image again and perform layout work, etc., and repeat the proof and check it. When the client's consent is obtained, the proofreading is completed and printing is performed by this machine.

[0010]

However, it is usually necessary to repeat proof printing until the client's consent is obtained. The film used for proofs is relatively expensive,
There is a problem that the cost increases as the number of proofs increases.

From this point of view, recently, in a DTP system, a color printer is used to perform proof printing as an alternative. In the personal computer system used for DTP, a so-called color management system is becoming standard as a function of OS (Operating System). Instead of conventional proof printing and color tone checking by a flatbed proofing machine, digital It is possible to create proofs in colors close to those printed by this machine with a printer.

Color management system (hereinafter referred to as "C
Also called "MS". ) Means that when there are multiple printing devices (collectively referred to as “devices”) such as scanners, printing machines, and digital printers, among these devices,
This is a function to achieve output color matching. Normally, when the same image data (for example, CMYK color data) is output by different devices (for example, printing and electrostatic copying), the colors of the actually obtained output products are different. This is because the color description CMYK does not directly describe the color represented by human senses but only the output signal of the device, and CMYK and RGB are, so to speak, “device dependent. It can be called "color". On the other hand, the absolute “color expressed as a human sense” is C
Standard color space defined by IE (International Commission on Illumination) (XY
It can be described by Z or L * a * b *). The function of the CMS is to describe in advance which color in the standard color space the colors such as CMYK and RGB of each device correspond to, descriptive data called a profile (conversion parameter used when performing color conversion. It is possible to obtain an output product of the same color on different devices by performing color conversion on the image while referring to the profile.

Therefore, by using the CMS function in the DTP system, the same color as the color when the printed matter is actually printed is reproduced and output by the color printer, and the proof print is created by the flatbed proofing machine. Alternatively, color printers can alternatively produce proofs.

However, there is no problem in the case of a normal process printed matter, but in the case of performing proof printing by using the color management function in the DTP system for special color printing (printed matter of single color or two colors), it is registered in the profile. Problems arise with the number of colors that are present. The color management function of the DTP system has a profile of 4 colors or 3 colors, because an image normally used is an image of 4 colors or 3 colors.
Only color devices can be handled. Therefore, in the case of special color printing such as two-color printing, since the color data described in the profile is only for two colors, the color management function of the DTP system cannot be used as it is. Therefore, the color management function cannot be used in spot color printing such as a two-color printing leaflet, and color calibration by a flatbed proofing machine is still required, which is an obstacle to high cost and time reduction.

An object of the present invention is to provide an apparatus capable of checking a color tone of special color printing by creating a proof by a color printer by using a process plate making system and a color management system.

[0016]

According to a first aspect of the present invention, in a method of creating a profile for special color printing used for color conversion by a color management system,
Of the four color plates of cyan, magenta, yellow, and black, a step of outputting a color chart obtained by a combination of plates used in the special color printing, and a value indicating each color in a standard color space for each color of the color chart. Measuring the combination of the L * value, the a * value, and the b * value, and for each color of the color chart, the combination of the cyan, magenta, yellow, and black values that make up each color plate, and the L * value, a *
And a step of converting the lookup table into a binary format lookup table according to a profile format. Constitute.

According to the above method, first, a color chart obtained by combining the colors used in the special color printing among the four color plates of cyan, magenta, yellow and black is output, and then the color chart. For each color, a combination of L *, a *, and b * values, which are the values that represent each color in the standard color space, is measured.
Next, for each color of the color chart, a look showing the correspondence between the combination of the cyan, magenta, yellow, and black values forming each color and the combination of the L * value, a * value, and b * value of each color. A look-up table is created, and then the look-up table is converted into a look-up table in binary format according to the format of the profile.

According to a second aspect of the present invention, in the method according to the first aspect, the step of creating the lookup table includes a one-dimensional lookup table for each of the cyan, magenta, yellow and black colors. Creating a look-up table from four dimensions to three dimensions showing the correspondence between the combination of the four colors of cyan, magenta, yellow and black and the combination of the L * value, a * value and b * value, Of the four colors, all values in the one-dimensional lookup table for colors other than the color used in spot color printing are set to 0. As a result, the values in the lookup table from 4D to 3D are not referenced for colors other than the colors used in spot color printing. Can be created.

According to a third aspect of the present invention, in the method according to the first aspect, the step of creating the look-up table includes a combination of the four colors of cyan, magenta, yellow and black and the L * value, A four-dimensional to three-dimensional lookup table showing a correspondence with a combination of a * value and b * value is created, and in the four-dimensional to three-dimensional lookup table, a special color among the four colors is created. The correspondence between the combination of colors used in spot color printing and the combination of the L * value, a * value, and b * value is the same for all values of colors other than the colors used in printing. As a result, the correspondence relationship between the combination of colors used in spot color printing and the combination of L * value, a * value, and b * value in the standard color space is the same regardless of the value of the color not used in spot color printing. Therefore, although there are four colors in the format, it is possible to create a profile for special color printing in terms of content.

According to a fourth aspect of the present invention, in a proof printing preparation apparatus for a spot color printing original, a spot color printing profile from a target spot color printing color is output by using a spot color printing profile and an output printer profile by color management processing. And a means for converting the color data into a proof copy by printing the color data obtained by the converting means using the color data printing device.

According to the above-described proof printing preparation apparatus for a spot color printing original, the color data is converted from the target spot color printing color to the output printer color by using the spot color printing profile and the output printer profile by the color management process. To be done. Further, the color data printing apparatus is used to print the color data obtained by the converting means, thereby producing a proof copy of the printed matter.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be described below with reference to the drawings.

First, before explaining the apparatus of the present invention, CM
The principle of S and the format of the profile used for it will be described.

The profile is a conversion parameter for converting the color of a specific device (for example, offset printing machine, color printer, etc.) into the standard color space (L * a * b *) described above. I for the format of the profile
It is being standardized internationally by an organization called CC (International Color Consortium) (ICC Profile Spec
See ification). The color space (L * a * b *) is a chromaticity diagram called CIELAB recommended by CIE, where L * represents lightness, a * represents the degree of red or green,
b * represents the degree of yellow or blue.

An outline of the contents of the profile defined by the ICC is shown in FIG. As shown in FIG. 1, the basic configuration of the portion for describing the color characteristics of the device has an n-dimensional → three-dimensional or three-dimensional → n three-dimensional lookup table (hereinafter also referred to as “LUT”). It is a LUT format of dimensions (n is the number of colors). That is, the n-dimensional → three-dimensional profile is
Correspond the n-dimensional color notation of a specific device to the standard 3-dimensional color space (L * a * b *). A three-dimensional → n-dimensional profile is a standard three-dimensional color space (L * a * b *)
Corresponds to the n-dimensional color notation of a particular device. The front and rear one-dimensional LUTs are usually linear (the input and output values are the same), but they may be set to have special characteristics and used to correct the temporal variation of the device. In FIG. 1, the LUT format of a three-color device (that is, n = 3) is illustrated in order to simplify the description.

The printing device type profile used in the present invention is an n-dimensional → three-dimensional LUT for converting the device color notation into the standard color space notation, and a pair of the standard color space to the device Three-dimensional conversion to color notation → n
This is a format including a dimension LUT.

FIG. 2 shows a method of using the profile of the print type device having the above-mentioned format for color conversion in CMS. If the color of one printing type device (eg offset printing machine, CMYK four colors) is reproduced on another printing type device (eg digital printer, CMYK four colors), and this is used as a proof (proof), the target profile of the conversion The profile of the offset printer is designated as, and the profile of the digital printer is designated as the profile of the device that reproduces the target color (hereinafter, referred to as “proof profile”). Then CMS
For the color data of a given image, using the 4D → 3D LUT of the profile of the target offset printing machine, determine where the color notation in offset printing is located in the L * a * b * space. calculate. Next, CMS describes the device color notation of the digital printer that reproduces this color.
Digital printer profile 3D → 4D LU
Calculate using T. In the actual color conversion of CMS, various contrivances have been made in order to speed up the calculation, but the basic principle is the above-mentioned mechanism.

Next, a method of creating a two-color printing profile according to this embodiment will be described with reference to FIG. The profile used for color conversion is created as follows.

First, a film output and a printing plate of a color chart image made by a combination of step scales of two plates (for example, C and M) used for a desired two-color printed matter are carried out,
This is printed with two target ink colors (for example, G and R).
Next, measure L * a * b * of each color of the printed color chart with a colorimeter, and display the device color notation C and M on the color chart.
A lookup table (LUT) of (printed colors are G and R) and measured values L * a * b * is created. An example of a part of this LUT is shown in FIG. In the table in the center of FIG. 4, CMY
Among the combinations of the data of the four color plates of K, a set of measured values of L * a * b * is associated with the C and M plates that are actually printed. In this way, a list of L * a * b * measurement values is created for all the colors on the color chart.

Next, a profile is created as shown in FIG. 3 based on the created list. The profile format is a one-dimensional LUT, four-dimensional → three-dimensional L as shown in FIG.
UT, one-dimensional LUT, but the first one
The dimension LUT has linear characteristics only for the colors to be used (C and M in this example), and the values of the LUTs for other colors are all zero. Also, in the 4-dimensional to 3-dimensional LUT, the measured L * a * b * measurement values are placed at the positions of the values corresponding to the combination of colors (C, M) used in two-color printing, and at the other positions. Inserts appropriate dummy data. The portion in which the dummy data is inserted, that is, the portion including the combination of the unused colors (Y, K) is not referred to because 0 is set in the preceding one-dimensional LUT, and therefore, what value is used? You can put it in. Also, the final one-dimensional L
All UTs have linear characteristics.

In this way, a profile for converting the data for two-color printing of the process printing machine into the standard color space can be created. This profile contains data of two colors (here, C and M) for two-color printing, and dummy data is added to Y and K to match the standard profile format, and four-color input is performed. The format is configured. Therefore, the data actually contained is for two-color printing, but since the format is four-color, color conversion can be performed by the normal CMS function.

Recently, software for creating a profile is also commercially available, and it is possible to create a profile for two-color printing by using this software. In that case, only the colors (for example, C and M) to be used for two-color printing out of the four-color chart are output on a film, and a proof is made by a flatbed proofing machine. Alternatively, the color chart may be printed by actually using a printing machine. And
The color chart is measured with a measuring instrument, and the measured value is input to the profile creation software. As a result, it is possible to create a profile for two-color printing, although the profile configuration has four colors.

In the case of special color printing plate making in the DTP system, it is possible to make a profile as described above and make a proof print with a digital printer using the color management function to check the color tone.

Next, with reference to FIGS. 5 and 6, the structure and operation of the spot color print creating apparatus according to the present invention will be described.
FIG. 5 shows an outline of the spot color print creating apparatus, and FIG. 6 shows its operation flowchart.

In FIG. 5, the spot color print creating apparatus comprises a scanner 10, a database 11, a DTP system 13, a digital color printer 14, an imagesetter 15, a plate making apparatus 16 and a flatbed proofing machine 17.

The scanner 10 is used to obtain corresponding color data from a required image, and the database 11 stores color data of various images and illustrations. DT
The P system 13 is a system with a CMS function,
Color conversion and control of the digital color printer 14 are performed.
Further, an image setter 15, a plate making device 16, and a flatbed proofing machine 17 are provided for making a proof print of the final plate when the correction of the proof print is completed.

The CMS function of the DTP system 13 performs color conversion for converting the color data of the two-color printing of the process printing machine into the data of the color printer 14. That is, the CMS function uses the profile for two-color printing described above to convert the two-color print data of the process printing machine into the standard color space (L * a * b).
*) Data, and using the profile of the color printer, the standard color space data is converted into the color notation of the color printer 14. As a result, the colors of the two-color printed matter of the process printing can be reproduced by the color printer, and the proof of the two-color printed matter can be created by the color printer. The profile for converting the two-color print data of the process printing machine into the data of the standard color space is created by the method described with reference to FIG. On the other hand, as the profile for converting the data in the standard color space into the color notation of the color printer 14, a profile created based on the four-color color chart output from the color printer 14 is used.

Next, the operation of the spot color print creating apparatus will be described with reference to FIG. First, the operator lays out the data obtained by using the scanner 10 or the data stored in the database 11 by the DTP system 13, and further synthesizes necessary documents, characters and the like to produce an original of a two-color printed matter. Create (steps S1, 2).

Next, the color data of this original is color-converted by CMS (step S3). That is, the two-color printing profile shown in FIG. 3 is used to convert the original of the two-color printed matter into the data of the standard color space, and further the profile for the color printer is converted into the data of the color printer. . Then, the color printer 14 prints the converted data. Although the data obtained in step S3 is expressed in color on the color printer, the color represented by the data is the same as the color of the two-color printing original as a result of color conversion. Therefore, the print result obtained in step S4 has the same color as the original two-color printing original, and is a proof copy of the two-color printing original created by the color printer.

Next, proofreading work is carried out by the proof print made by this color printer, and if necessary, step S
The procedure is returned to step 1 and S2 to perform the editing work, and the corrected proof is prepared by the color printer. This process is repeated until the proofreading is completed, and the proof print repeatedly created during that time is created by the color printer 14. When the proofreading is completed, a proofing film is created by using the imagesetter 15, and the flatbed proofing machine 16 creates a final proofprint.

As described above, of the proofs that are usually performed a plurality of times, only the final version is prepared by the flatbed proofing machine, and the proofs before that are prepared by the color printer, so that an expensive film is used. It is possible to make only one proof print by the flatbed proof machine. The cost of proof printing by a color printer is much lower than that of proof printing by a flatbed proof machine, and the labor cost can be reduced. Therefore, the cost required for proofreading can be greatly reduced. In addition, it is possible to shorten the time for creating a proof. Furthermore, for print items that do not require precise proof printing, it is possible to omit the production of proof printing by a flatbed proofing machine and start the printing process after the completion of color printing.

Next, another embodiment of the two-color printing profile created and used according to the present invention will be described with reference to FIG. In the two-color printing profile shown in FIG. 3, the one-dimensional LUT corresponding to the unused colors (Y and K in this example) is set to 0, and the position of the combination including those colors in the four-dimensional → three-dimensional LUT is set. It contains dummy data. In the first-stage one-dimensional LUT, since the Y and K LUTs are all 0, the dummy data portion is not referred to, and as a result, the contents of only two colors are included.

On the other hand, in the embodiment shown in FIG. 8, the contents of the one-dimensional LUT in the first stage are linear for all colors, and in the four-dimensional → three-dimensional LUT in the next stage, all the Y values are different. Put the same C and M values. That is, in the schematic view of FIG. 8, the same two-dimensional LUT as the two-dimensional LUTs of C and M on the forefront are used for all Y's to create a four-dimensional → three-dimensional LUT. Although it is not illustrated at the same time because it has four dimensions, K has the same configuration as Y.

According to this, since the same L * a * b * value is determined irrespective of the values of Y and K by the combination of the values of C and M, the same output as in the case of FIG. 3 is obtained. be able to.

Next, an application example of the present invention will be described with reference to FIG. In this application example, a plurality of DTP systems are connected to a network, and proofs made at a specific place are transmitted to a system at another place on the network. In the system that has received the proof, the proof can be output by a color printer using the received data to perform the proof work.

In the above-mentioned ICC profile specification, it is possible to attach a target profile of specific image data to the specific image data. Utilizing this function,
A two-color printing profile according to the present invention is attached to data created by DTP and transmitted to a remote place. The receiving side can output a proof copy using the CMS function by using the transmitted image data, the attached two-color printing profile and the profile of the color printer of its own system.

According to this method, it is not necessary to bring the output proof to the requestee, so that the labor cost can be reduced. Also, since the output printer is set on the receiving side, it is not necessary for the transmitting side to make settings related to the profile of the printer used for output, and no matter what printer the receiving side has, that printer can be used on the receiving side. You can use the profile. Therefore, proof printing data can be transmitted to a remote place without being restricted by the printer that outputs the proof.

In the above description, two-color printing was mentioned as an example of spot color printing, but the present invention is not limited to this.
It can be applied when printing is performed with a special color (different from normal YMCK or RGB) single color or three colors.

[0049]

According to the first aspect of the present invention, a profile for special color printing is created even though it has four colors in the structure. Therefore, the color management function can be used by using this profile. With this, it is possible to create a proof copy for special color printing with a color printer or the like.

According to the second aspect of the present invention, for the colors other than the colors used in the spot color printing, the values in the look-up table from the 4th dimension to the 3rd dimension are no longer referred to. However, it is possible to create a profile for spot color printing in terms of content.

According to the third aspect of the present invention, the L * value, the a * value, and the b value in the standard color space and the combination of the colors used in the special color printing are irrespective of the values of the colors not used in the special color printing. * Since the correspondence with the combination of values is the same,
Although there are four colors in the form, a profile for special color printing can be created in terms of content.

According to the fourth aspect of the present invention, a proof print of a special color printing original can be created by using a color data printing device such as a color printer, and the cost and time required for the proof print can be reduced. can do.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a profile format used in a color management system.

FIG. 2 is a diagram showing an outline of processing in a color management system.

FIG. 3 is a diagram schematically showing a configuration of a two-color printing profile according to the present invention.

FIG. 4 is a diagram showing a method of creating a two-color printing profile.

FIG. 5 is a block diagram showing a configuration of a two-color print creating apparatus according to the present invention.

6 is a flowchart showing the operation of the apparatus shown in FIG.

FIG. 7 is a diagram showing an application example of a two-color print creating apparatus according to the present invention.

FIG. 8 is a diagram schematically showing the configuration of another example of a two-color printing profile.

FIG. 9 is a block diagram showing a configuration of a conventional spot color print creating apparatus.

10 is a flowchart showing the operation of the apparatus shown in FIG.

[Explanation of symbols]

10, 50 ... Scanner 11, 51 ... Database 13, 52 ... DTP system 14 ... Color printer 15, 53 ... Imagesetter 16, 54 ... Plate-making device 17, 55 ... Flatbed calibration machine

Claims (4)

[Claims] 1. A method for creating a profile for special color printing used for color conversion by a color management system, wherein a color chart obtained by combining the plates used for special color printing among four color plates of cyan, magenta, yellow and black. And a step of measuring, for each color of the color chart, a combination of L * value, a * value, and b * value that are values indicating each color in a standard color space, and for each color of the color chart , Creating a look-up table showing the correspondence between the combinations of the values of cyan, magenta, yellow, and black constituting each color plate and the combinations of the L * value, a * value, and b * value of each color, A process for converting the lookup table into a binary lookup table according to the profile format. And, a method having the. 2. The step of creating the look-up table includes a one-dimensional look-up table for each of the cyan, magenta, yellow and black colors, a combination of the four colors of cyan, magenta, yellow and black and the L A four-dimensional to three-dimensional lookup table showing the correspondence with the combination of * value, a * value, and b * value is created, and the look-up table of the four colors other than the color used in the special color printing is created. The method of claim 1, wherein all values in the one-dimensional lookup table are zero. 3. The step of creating the look-up table shows a correspondence between the combination of the four colors of cyan, magenta, yellow and black and the combination of the L * value, a * value and b * value. A lookup table from 4 dimensions to 3 dimensions is created, and in the lookup table from 4 dimensions to 3 dimensions, the special color is applied to all values of colors other than the colors used in the special color printing among the 4 colors. The correspondence relationship between a color combination used in printing and the L * value, a * value, and b * value combination is the same.
The method described in. 4. A unit for converting color data from a target spot color printing color to an output printer color by using a spot color printing profile and an output printer profile by color management processing, and using the color data printing device. And a means for creating a proof copy of the printed matter by printing the color data obtained by the converting means.