JP2001086357A - Color-proofreading system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain proofreading by using binary dot image data that have been subjected to RIP. SOLUTION: This system is provided with an image data processing part 1 composed of a microcomputer system, etc., and an outputting part 2 composed of an inkjet color printer, etc., and the part 1 has a multi-level data converting means 3, a gradation conversion means 4 and an error diffusing means 5. The means 3 converts binary dot image data, that are indicated by '0' or '1' and which have been subjected to RIP, into multi-level data. The means 4 performs conversion processing of image data converted into the multi-level data with a conversion table obtained by preliminarily photometering a color chart and meets the color of the part 2 to that of a printer, etc. The means 5 conducts binary coding of multi-level image data that have been subjected to gradation conversion. Pixels are given at random as error diffusion processing here, and a halftone gradation can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color proofing system capable of obtaining a color proof from RIP-converted image data.

[0002]

2. Description of the Related Art In a printing / plate making process, a proofreading operation is performed before a final printing process to check whether or not a prepared printing plate is surely made. In this proofreading work, conventionally, a printing plate for proofreading different from that for main printing was prepared, and a test print called proof print was prepared using a proofing machine or the like. Then, by inspecting the proof print, for example, the color condition of the printed matter and the like were confirmed.

On the other hand, in recent years, the plate making process has been carried out by digital processing using a computer as called DTP. Therefore, in plate making of a printing plate, for example, image data of an original plate is converted into binary image data obtained by halftoning by RIP conversion or the like, and the printing plate is digitally made using the binary image data. A digital plate making apparatus called a so-called CTP has been developed. Such a digital plate making apparatus has an advantage of not using an intermediate product such as a plate making film.However, in the proofing work, a proof print is directly produced from the image data without preparing a printing plate or a plate making film for proof. There was a request to get it.

[0004]

As a method of easily obtaining a proof print from image data, for example, there is a method of outputting image data created by the DTP using a color printer or the like. Although this method has an advantage that a proof print can be easily obtained, it has a drawback that accurate color proofing cannot be performed because the color of the printed matter is different between the ink color of the main printing and the ink color of the color printer. For this reason, when performing accurate color proofing, it is necessary to perform color gradation conversion called color matching that matches a color reproduced by a color printer to a printing press.

However, in the digital plate making apparatus, since the printing plate is exposed by an on / off-modulated laser or an LED light source, the RIP-converted image data is binary image data corresponding to the on / off. There is a problem that the gradation conversion cannot be performed.

Therefore, conventionally, multi-value image data before RIP conversion is subjected to gradation conversion according to a color printer, and the gradation-converted multi-value image data is RIP converted and output to a color printer or the like. Was. However, in the above method, RIP conversion is required twice for proofing for outputting to a color printer and for main printing for making a printing plate, and the entire processing time is required.

The present invention solves the above-mentioned problems, and can use binary image data that has already been RIP-converted and halftone-dotted, and is capable of performing calibration output to output means such as a color printer. The purpose is to provide a system.

[0008]

According to a first aspect of the present invention, there is provided a binary image processing apparatus in which a value of each pixel constituting a halftone dot is subjected to RIP conversion and represented by a binary value of "0" or "1". A color proofing system for outputting a color image using image data for four colors of YMCK, wherein the pixel of "0" is set to "0" and the pixel of "1" is set to a predetermined value "n (where n>
Multi-value conversion means for converting binary image data into multi-value image data of "0" or "n",
The multi-valued image data is corrected for each pixel coordinate in accordance with the ink color used in the output, and the “0” or “n” is corrected.
Gradation conversion means for converting each of the image data into a predetermined value from "0" to "n";
Reconverts to binary image data that determines whether to output a corresponding pixel in accordance with a multi-valued value from “n” to “n”.
Value conversion means; and output means for outputting a color image based on the re-converted binary image data.

According to a second aspect of the present invention, in the first aspect of the present invention, the gradation conversion means is arranged such that a pixel value for each YMCK is (Y, M, C, K) = (Ay, Am , A
c, Ak) is represented by (Y, M, C, K) =
A conversion table for converting the image data into (By, Bm, Bc, Bk) is provided. (However, Ay, Am, Ac,
Ak is a value of 0 or n, respectively, and By, Bm, B
c and Bk are any values in the range of 0 to n)

According to a third aspect of the present invention, in the second aspect of the invention, the conversion table is created by taking in data obtained by measuring the color chart of the color chart output by the output means in advance.

According to a fourth aspect of the present invention, in the first aspect of the present invention, when the value of the pixel of the image data exceeds a predetermined threshold value, And performs error diffusion processing for distributing the difference between the value of the image data and the threshold value to the pixel at the next coordinate or the value of surrounding pixels.

According to a fifth aspect of the present invention, in the first aspect of the present invention, the color of a predetermined printing paper is measured in advance and the ground color image data of the printing paper is stored. If the YMCK values of the binary image data are all "0", the image data is converted in correspondence with the ground color image data.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of a color proofing system according to an embodiment of the present invention will be described below with reference to FIG. FIG. 1 is a block diagram showing an example of a color proofing system according to the present invention.

In the figure, a color proofing system according to the present embodiment includes an image data processing unit 1 for processing image data, and an output unit 2 for printing based on the image data processed by the image data processing unit 1. Consists of

The image data processing section 1 comprises a microcomputer system provided with various input / output means and storage means. Functionally, the RIP-processed binary halftone image data is transferred to a CTP system. Conversion means 3 which receives from an image processing device of the type and converts it into a multi-value
A gradation conversion means 4 for performing gradation conversion of the multi-value converted image data for each coordinate of each pixel in accordance with an ink color used in the output unit 2; Error diffusion processing means 5 for performing diffusion processing to convert the image data into binary image data that determines on / off of pixels.

The output unit 2 is a color printer capable of outputting an image using four colors of YMCK ink. In the present embodiment, the output unit 2 comprises an ink jet type color printer. The output unit 2 composed of the ink jet type color printer can express a halftone dot S for printing by a set of pixels due to adhesion of ink as shown in an enlarged manner in FIG.

In the following description, the image data of the pixel having the same coordinates (address) is represented by (Y, M, C, K) = (0,
1, 1, 0), and in this example, it indicates that pixels exist in the M and C planes at the corresponding coordinates.

Returning to FIG. 1, first, the multi-value conversion means 3
The binarized dot image data is converted into multi-values by software. In this embodiment, when the pixel value is “0”, the pixel value is converted to “0”, and when the pixel value is “1”, the pixel value is converted to “255”.
The image data is converted into multi-level image data of 256 gradations up to 5 ".

However, at this point, each pixel has substantially only a value of "0" or "255". For example, the multi-value conversion means 3 converts the image data (Y, M, C,
If (K) = (0,1,1,0), (Y, M, C, K)
= (0, 255, 255, 0). If multi-value conversion is performed on all coordinates, the next gradation conversion means 4 performs gradation conversion of each color.

The gradation conversion means 4 performs gradation conversion of the multi-valued image data in the preceding stage using a conversion table described later. Specifically, the gradation conversion means 4 has a value of either "0" or "255". The value of the image data that has been lost is corrected to any value in a range from “0” to “255”. That is, the conversion table sets Ay to Ak to a value of “0” or “255” and sets By to Bk to “0”.
, The image data (Y, M, C, K) = (Ay, Am, Ac, Ak) is converted to (Y, M, C, K) = (By, Bm, Bc, Bk).

FIG. 2 shows an example of such a conversion table. In this conversion table, Ay to Ak are “0” or “2”.
The data is tabulated for all combinations that take any one of "55".

Hereinafter, a method of creating the conversion table will be described. In this embodiment, first, a color chart in which the output unit 2 outputs each color of YMCK for each of a plurality of gradations is prepared. For example, since the gradation value of each pixel of YMCK has a range from “0” to “255”, if the gradation value is divided into eight steps for each “32”, for example, YMCK
For each of the four colors of CK, a color chart of 8 to the fourth power = 4096 colors is obtained for each of eight steps.

The output unit 2 used in the present invention
Is for forming pixels with four colors of YMCK ink, and the intermediate gradation is represented by the number of pixels output within a predetermined area. That is, gradation is expressed by changing the occurrence probability of pixels.

Next, this color chart is measured by a colorimeter.
Colorimetrically measure, for example, L ^*A^*B^*Color system
Measure the value. Thereby, as shown in FIG.
L corresponding to each gradation of^*A^*B^*Numeric data based on color system
Data is obtained. Preferably the measured value of the colorimeter is directly
Or, indirectly, the image data processing unit 1
Store as first table data in a memory (not shown)
You.

Although this example shows an example in which each color is measured in eight steps for each "32" gradation, color measurement may be performed in any other number of steps. Then, the color system numerical value of the gradation between each stage is obtained by an interpolation operation.

Next, a printing machine used in the actual printing (hereinafter simply referred to as a printing machine) prints a color chart composed of the same image data, measures the color, and digitizes the color chart using the same L ^* A ^* B ^* color system. . Then, similarly, the image data is stored in the memory of the image data processing unit 1 as second table data. It is the same as above to obtain the gradation between image data by interpolation.

From these values, the conversion text as shown in FIG.
Create a cable. This conversion table is obtained after gradation conversion.
The print color output by the output unit 2 based on the image data is represented by the gradation
Printing on a printing machine based on image data before conversion
The image data before the conversion is converted to the color so as to match the color.
This is for replacing the image data with the replaced image data. concrete
Are the first table data and the second table data.
And L^*A ^*B^*The color system values are the best
The image data before conversion and the image data after conversion
Just turn it on.

In the present embodiment, as described above, the conversion table is created based on the colorimetric results, but the operator manually inputs data based on known color data of the corresponding ink. May be performed. Further, instead of adjusting the colors to the printing press, the colors may be adjusted to a predetermined standard color.

Further, the gradation conversion means 4 may be configured not to include the above-mentioned conversion table and to perform gradation conversion of the image data by calculation using a predetermined conversion function. However, in order to speed up the processing, it is preferable to replace the image data with the above-mentioned conversion table rather than the operation by the function.

On the other hand, when the main printing is the printing of a newspaper or the like, the printing paper (newspaper) has a darker background color than ordinary white paper. In such a case, even if the colors of the inks can be matched to some extent, the actually output printed matter looks different to human eyes. Therefore, it is preferable that the paper output by the output unit 2 such as a color printer is also given the same ground color.

In the color proofing system according to the present embodiment, the ground color can be pseudo-matched by using the present invention. That is, in the conversion table of FIG. 2, image data (Y, M, C, K) = (0, 0, 0, 0) is converted to image data (for example, FIG. In the example of (Y, M, C, K) = (2, 5, 3,
0)), a ground color having the same hue as that of the printing paper for actual printing is formed on the background of the printing paper having no ink image. The image data corresponding to the ground color can be obtained by measuring the color of a non-image portion in the same manner as the image portion of the color chart.

In the reproduction of the ground color according to the present invention, a plurality of pixels d are scattered on the ground portion of the paper as shown in an enlarged view in FIG. 5, for example, and the same ground color appears to human eyes. .
The method for actually forming pixels will be described in the following error diffusion processing means 5.

Returning to FIG. 1, the error diffusion processing means 5 determines whether or not to output a corresponding pixel based on the multi-valued halftone image data gradation-converted by the gradation conversion means 4. "Or" 1 ".

First, it is determined whether the value of a pixel exceeds a predetermined threshold value for each predetermined coordinate and binarized. As an example, when the threshold is set to “240”, if the image data is (Y, M, C, K) = (5, 10, 245, 0),
The binarized image data is (Y, M, C, K) = (0,
0, 1, 0). That is, in this example, only the C color pixel is formed at the coordinates.

On the other hand, if the pixel value does not exceed the threshold,
The value is distributed to the value of the next pixel. For example, the image data (Y, M, C, K) = (5, 10, 245,
0), for the image data of the next pixel, +
For +5 and M colors, +10 is added, and the values are sequentially accumulated as long as the value does not exceed the threshold value. Therefore, image data having a value not exceeding the threshold value constitutes a pixel when the cumulative value reaches the threshold value. Thereby, pixels can be formed with a probability corresponding to the image data.

The accumulation of the pixel values may be distributed not only to the next pixel but also to a plurality of surrounding pixels in a predetermined distribution. Further, even with a value exceeding the threshold value, the difference between the value and the threshold value may be distributed to the next pixel or surrounding pixels.

If the image data is "1" based on the binary image data obtained by the error diffusion processing means 5, pixels of a corresponding color are formed and an image is output. When the output of the pixel is stochastically performed in this manner, FIG.
Thus, a halftone image S which looks like a halftone can be obtained. For example, in FIG. 4A, a halftone dot image of a lighter color can be formed because some images become blank, and FIG.
Indicates that a dot image of a different color can be formed by attaching a pixel of a different color.

[0038]

According to the first aspect of the present invention, the RIP
The converted binary image data can be used, and color proofing can be obtained after performing gradation conversion of a color according to the ink color of the output unit.

According to the second aspect of the present invention, color tone conversion can be performed by using a conversion table prepared in advance, so that processing can be performed at high speed.

According to the third aspect of the present invention, since the data obtained by measuring the color chart in the conversion table is taken in, accurate data input can be performed, and manual input is not required.

According to the invention described in claim 4, since the pixels can be output stochastically, an intermediate color tone can be reproduced.

According to the invention described in claim 5, the ground color of the printing paper can be reproduced.

[Brief description of the drawings]

FIG. 1 is a block diagram of a color proofing system according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a conversion table in the color proofing system.

FIG. 3 is an explanatory diagram of color measurement of a color chart for creating the conversion table.

FIG. 4 is an explanatory diagram of a halftone dot image in the color proofing system.

FIG. 5 is an explanatory diagram of a ground color formed in the color proofing system.

FIG. 6 is an explanatory diagram of a halftone image composed of pixels.

[Explanation of symbols]

 Reference Signs List 1 image data processing unit 2 output unit 3 multi-value conversion means 4 gradation conversion means 5 error diffusion processing means S halftone dot d pixel

Continued on the front page F term (reference) 2C262 AA02 AA24 AA29 AB13 BA09 BB03 BB08 BC01 EA10 EA11 FA13 FA18 GA03 5B057 BA30 CA01 CA07 CA12 CB01 CB07 CB12 CC01 CE11 CE12 CE16 CE17 CH07 CH18 5C077 LL12 MM11 MP02P08 NN11 RR07 RR14 TT08 5C079 HA19 HB03 LA21 LA31 LA33 LA34 LC09 MA04 MA10 NA03 PA07

Claims (5)

[Claims] 1. A color image is formed by using binary image data of four colors of YMCK, which is RIP-converted and binary image data in which the value of each pixel constituting a halftone dot is represented by a binary value of "0" or "1". A color proofing system for outputting, wherein the pixel of “0” is converted to “0”, the pixel of “1” is converted to a predetermined value “n (where n> 1)”, and the binary image data is converted to “ A multi-level conversion means for converting into multi-level image data of "0" or "n"; and correcting the multi-level image data for each pixel coordinate in accordance with an ink color used in output. "Or" n "
And gray scale conversion means for converting each of the image data into a predetermined value from "0" to "n", and a corresponding pixel according to a multi-valued value from "0" to "n" of the image data. A color proofing system comprising: binary conversion means for re-converting to binary image data for determining whether to output; and output means for outputting a color image based on the re-converted binary image data. 2. The image processing apparatus according to claim 1, wherein the value of the pixel for each of YMCK is (Y, M, C, K) = (Ay, Am, Ac, A).
k) is represented by (Y, M, C, K) = (B
2. The color proofing system according to claim 1, further comprising a conversion table for converting the image data into y, Bm, Bc, and Bk). (Where Ay, Am, Ac, and Ak are each 0 or n
Where By, Bm, Bc, and Bk are each 0 to n.
Any value in the range up to) 3. The color proofing system according to claim 2, wherein said conversion table is created by fetching data obtained by measuring colors of a color chart previously output by said output means. 4. The binary conversion means outputs a pixel at the coordinates when the value of the pixel of the image data exceeds a predetermined threshold, and outputs the pixel at the coordinates when the value of the image data does not exceed the threshold. 4. The color proofing system according to claim 1, wherein the color proofing system performs an error diffusion process of distributing the value to the value of a pixel at the next coordinate or the value of a surrounding pixel. 5. A method of measuring the color of a predetermined printing paper in advance and storing the image data of the ground color of the printing paper, and when the YMCK value of the binary image data is all "0", 5. The color proofing system according to claim 1, wherein data is converted in correspondence with said ground color image data.