JP3658255B2 - Color output method and color output device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a color output method or a color output apparatus capable of obtaining color calibration of a halftone image using a color drawing apparatus such as an ink jet printer.
[0002]
[Prior art]
In the printing / plate making process, before starting the final printing process, a proofreading operation is performed to inspect whether the created printing plate is definitely made. Conventionally, in this proofreading work, a test print called a proof print different from the main print has been created. Then, by checking the proof, for example, the color tone of printed matter, the correctness of characters, the position of an image, and the like have been confirmed.
[0003]
On the other hand, in recent years, the plate making process has been carried out by digital processing using a computer as called DTP. For this reason, even in the plate making of a printing plate, for example, an apparatus that converts original image data into binary image data by RIP processing or the like, and digitally makes the printing plate using the binary image data, so-called A digital plate making apparatus called CTP has been developed. In such a digital plate making apparatus, there is an advantage that an intermediate product such as a plate making film is not used, but even in the proofreading operation, a proof print is directly made from the image data without creating a proof printing plate or a plate making film. There was a request to get.
[0004]
As a method for easily obtaining a proof print from the image data as described above, for example, there is a method of outputting image data created by the DTP using a color printer such as an ink jet printer. Although this method has an advantage that a proof can be easily obtained, there is a disadvantage that accurate color proofing cannot be performed because the color of the printed matter differs between the ink color of the main printing and the ink color of the color printer. For this reason, when performing accurate color calibration, a color correction process called color matching that matches the color reproduced by the color printer with the printing machine is essential.
[0005]
[Problems to be solved by the invention]
In lithographic printing, the density of an image is generally expressed by halftone dots. For this reason, even in the final image data, image data obtained by binarizing a halftone image is used. For example, assume that a halftone dot image as shown in FIG. 5A is expressed by an ink jet printer. Here, the output part a1 is composed of a plurality of pixels (dots) output by the ink jet printer. Therefore, the output portion a1 actually outputs 100% of the pixels to form a halftone dot, and the non-output portion b has the output of the pixel set to 0%.
[0006]
However, when the halftone dot image is output by an ink jet printer or the like, the output portion a2 becomes larger due to the spread of ink as shown in FIG. 5B, and the overall color tone may change. To prevent this, the output pixels are thinned out by lowering the output probability of the pixels from 100% as in the output portion a3 shown in FIG. 5C, so that the human eye can see the same density macroscopically. can do.
[0007]
If this method is used, for example, when the hue of an ink jet printer is slightly less bluish than that of a printing machine for a certain color in which a halftone dot of three colors of cyan, magenta, and yellow exists at a predetermined ratio, cyan It is possible to perform color correction by slightly increasing the output probability of the pixels.
[0008]
However, in the correction as described above, correction is applied to all cyan, and there is a problem that color correction is applied to a place where correction is not desired.
[0009]
As one method for solving this problem, binary image data shaded by RIP processing is subjected to de-screening processing to make halftones, and each halftone color corresponding to each halftone color. A corresponding color correction may be performed. However, although this method can correct the color, there are problems that halftone dot information is lost from the image data and fine details such as characters are lost.
[0010]
SUMMARY OF THE INVENTION An object of the present invention is to provide a color output method and a color output apparatus that can solve the above problems and can perform color correction for each color while leaving halftone dot information.
[0011]
[Means for Solving the Problems]
The invention according to claim 1 is a color output method for outputting a color halftone image by pixel output of a plurality of colors using binary image data representing a halftone image, wherein the binary image data is descreened. Converting to multi-value image data, obtaining color correction data corresponding to the coordinate position of each pixel based on the multi-value image data, and corresponding the binary image data to the coordinate position of each pixel. The method includes a step of performing color correction using the color correction data thus converted into color-corrected image data, and a step of performing color output using the color-corrected image data.
[0012]
According to a second aspect of the present invention, in the first aspect of the invention, the color-corrected image data is subjected to error diffusion processing to perform color output.
[0013]
According to a third aspect of the present invention, in the first or second aspect of the present invention, the color correction data is determined based on a color correction table prepared in advance according to an output device to be used.
[0014]
According to a fourth aspect of the present invention, in the third aspect of the invention, the color correction table includes color correction data to be added to or subtracted from the multivalued image data representing the predetermined color. Assigned.
[0015]
The invention according to claim 5 is a color output method for outputting a color halftone image by pixel output of a plurality of colors using binary image data D shaded by RIP processing, wherein the binary image Converting each value of the data D from binary to multi-value to obtain first image data Do in which each pixel value is pseudo multi-value; and descreening the first image data Do Then, referring to a step of converting each pixel value into second image data Dd having an intermediate value and a color correction table prepared in advance, each pixel coordinate position corresponds to the second image data Dd. Obtaining color correction data Dc, and obtaining third image data Dx obtained by performing color correction by adding / subtracting the first image data Do and the color correction data Dc for each coordinate position of each pixel; , Error diffusion of the third image data Dx A step of converting the substantially binary Fourth image data Dz and management, and outputting a color halftone image by said fourth image data Dz, consists.
[0016]
The invention according to claim 6 is a color output device for outputting a color halftone image by pixel output of a plurality of colors using binary image data shaded by RIP processing, wherein the binary image data Data processing means for performing color correction while maintaining the halftone dot information and converting it into multi-valued image data, and based on the color-corrected multi-valued image data, it can take either binary data for drawing or non-drawing. Output means for outputting pixels and outputting a color image.
[0017]
According to a seventh aspect of the invention, in the sixth aspect of the invention, the data processing means intermediately generates multi-value image data having no halftone information from the binary image data.
[0018]
The invention according to claim 8 is the invention according to claim 7, wherein the data processing means converts each value of the binary image data from binary to multi-value, and the value of each pixel is pseudo. Multi-value conversion means for obtaining first multi-value image data, and de-screening means for de-screening the first image data and converting the first image data into second image data having an intermediate value for each pixel A color correction table for obtaining color correction data for each coordinate position of each pixel based on the second image data, and the first image data and the color correction data for each coordinate position of each pixel. And color correction means for obtaining third image data subjected to color correction. Further, either the data processing means or the output means performs error diffusion processing on the third image data. The fourth image that is substantially binary It comprises an error diffusion processing means for converting the over data.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
The configuration and operation procedure of the color output apparatus according to the embodiment of the present invention will be described below with reference to the block diagram of FIG. 1 and the flowchart of FIG.
[0020]
In FIG. 1, the color output apparatus according to the present embodiment includes a data processing unit 1 that processes image data, and an output unit 2 that performs color output based on the image data processed by the data processing unit 1. .
[0021]
The data processing means 1 is composed of a microcomputer provided with various input / output means, display means, storage means, etc., and the output means 2 is a pixel of at least three colors of c (cyan), m (magenta), and y (yellow). In this embodiment, a printing apparatus capable of outputting a color image by outputting or outputting four colors of pixels including k (black), for example, a color ink jet printer is assumed.
[0022]
In terms of functional blocks, the data processing means 1 receives the image data D binarized by the RIP means 10 such as a CTP output machine arranged in the previous stage, and multi-values it pseudo-converts it into multi-value image data Do. A conversion unit 11; a descreening unit 12 for descreening the multi-valued image data Do to convert it into image data Dd having a halftone; and a color for obtaining color correction data Dc based on the descreened image data Dd Correction table means 13, color correction means 14 for color-correcting the image data Do based on the color correction data Dc to output color-corrected multi-value image data Dx, and color-corrected multi-value image data Dx And error diffusion processing means 15 for converting the image data into binary image data Dz.
[0023]
Next, the data processing procedure of the data processing means 1 will be described with reference to the flowchart of FIG. 2 in accordance with the detailed description of each block.
[0024]
First, in step S1 of the flow, the binary image data D is artificially converted into a multi-value by the multi-value conversion means 11 and stored in a predetermined storage device or the like. For example, in the case of binary image data raster-converted by the RIP unit 10 in the previous stage, “1” or “0” represents that a pixel is output or not output, but the value “ 1 ”is converted to“ 100 ”. Thereby, although it is substantially any value of “0” or “100” at this stage, the pseudo multi-valued image data Do that can take a halftone between 0 and 100 is obtained. It has been converted. Note that the numerical value “100” may be set to other values according to the number of gradations that can be set.
[0025]
Next, in step S2, the descreening means 12 descreens the multivalued image data Do and converts it into multivalued image data Dd including halftone values. This descreening process is generally achieved, for example, by averaging pixel values in a predetermined range by a filter having a predetermined size. Note that the multi-value image data Do before conversion is left in the storage device separately for use in the process of step S4.
[0026]
A halftone image before this descreening process is considered, for example, using a model shown in FIG. In FIG. 3A, for the sake of easy understanding, one halftone dot is formed by four pixels for convenience, and c (cyan), m (magenta), and y (yellow) are arranged to have different screen angles. In this example, halftone dots of the three colors are uniformly formed. In FIG. 3A, a pixel painted black is represented by c color, a pixel hatched by diagonal lines is represented by m color, and a pixel hatched by stippling is represented by y color.
[0027]
In this example, since three colors are evenly mixed, it is perceived as a gray color having an appropriate density on a macro basis. However, microscopically, for example, only the cyan ink pixel is drawn at the coordinate position of the target pixel P, and the image data at this coordinate is (c, m, y, k) = (100, 0, 0, 0). ).
[0028]
FIG. 3B shows a state in which the halftone image shown in FIG. 3A is descreened. In FIG. 3B, since the pixel values around a predetermined area are averaged, the image data at the coordinate position of the target pixel P is, for example, (c, m, y, k) = (25, 25, 25, 0) and expressed in halftones. The image data Dd generated by this descreening process loses halftone dot information, and fine details such as characters are lost.
[0029]
In the next step S3, color correction data Dc corresponding to the descreened image data Dd is determined for each pixel coordinate using a predetermined color correction table 13. An example of the color correction table 13 is shown in FIG. In this example, a table in which the value of each color of cmyk is different by 10 gradations is used, but it may be set for each appropriate gradation. Note that intermediate value image data not corresponding to the values in this table is determined by a general interpolation calculation.
[0030]
The color correction table 13 is created in advance as follows, for example. First, a color chart is printed for each predetermined gradation by an ink jet printer to be used and a reference printer. Next, the color of the color chart is measured, and color correction data Dc is obtained so that the colors printed by the ink jet printer and the printing press have the same hue.
[0031]
For example, taking the table shown in FIG. 4 as an example, the color printed with image data Dd (c, m, y, k) = (10, 10, 10, 0) on the reference printing press is an ink jet. Assuming that the printer outputs substantially the same color as the image data Dd (c, m, y, k) = (8, 5, 11, 0), the color correction data Dc is the difference (c, m) of the image data. , Y, k) = (− 2, −5, +1, 0). That is, when printing with image data Dd (c, m, y, k) = (10, 10, 10, 0) in an ink jet printer, color correction data Dc (c, m, y, k) is added to the image data. By adding = (− 2, −5, +1, 0), image data corrected to the same color as the reference printing press can be obtained.
[0032]
In the next step S4, color correction is performed using the color correction data Dc obtained in step S3. The image data to be subjected to this color correction is image data Do having halftone dot information. That is, in step S4, the color-corrected image data Dx is calculated by adding the color correction data Dc to the image data Do before being descreened for each pixel coordinate.
[0033]
For example, in the example of FIG. 3, the target pixel P has the image data Do before being descreened as (c, m, y, k) = (100, 0, 0, 0), and the image data Dd after being descreened. (C, m, y, k) = (25, 25, 25, 0), and color correction data Dc corresponding to the image data Dd is taken as an example (c, m, y, k) = (− 10, Assuming −5, 0, 0), the color-corrected image data Dx is calculated by Dx = Do + Dc to be (c, m, y, k) = (90, 0, 0, 0). For m, the actual calculation result is −5, but since the gradation in this example is set from “0” to “100”, it is corrected to “0”.
[0034]
In the present invention, as described above, the color correction data is obtained based on the descreened image data Dd, and the obtained color correction data is applied to the image data Do before being descreened. Accurate color matching can be performed for each color without losing information.
[0035]
Since the color-corrected image data Dx includes multi-valued intermediate values, the binary image data Dz is again used in order to correspond to an ink jet printer that records an image with binary values of whether or not to output ink dots. Must be converted to In the next step S5, this conversion is achieved by error diffusion processing. Note that although error diffusion processing is performed in the present embodiment, other binarization processing including dithering processing may be employed.
[0036]
For example, in the case of (c, m, y, k) = (90, 0, 0, 0), the pixel of interest P is output with a probability of 90%, in other words, one pixel is missing every 10 pixels. You can make it. In the error diffusion processing, when the pixel value exceeds a predetermined threshold, the pixel is output, and the error is generated between the threshold and the next pixel or surrounding pixels in order to achieve the above method. . In the present embodiment, the error diffusion processing is arranged in the data processing means 1, but it may be arranged on the output means side such as an ink jet printer.
[0037]
In step S7, pixels are output according to the image data Dx converted to binary by the error diffusion process, and the printing of the image is completed.
[0038]
【The invention's effect】
In the present invention, since color correction can be performed for each color while leaving halftone dot information, color calibration that is color-matched to the printed material can be easily obtained.
[Brief description of the drawings]
FIG. 1 is a block diagram of a color output apparatus according to an embodiment of the present invention.
FIG. 2 is a flowchart showing a color output procedure in the color output apparatus.
FIG. 3 is a diagram for explaining a descreening process in the color output device.
FIG. 4 is a view showing an example of a color correction table used in the color output apparatus.
FIG. 5 is a diagram for explaining halftone dot output in an ink jet printer.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Data processing means 2 Output means 10 RIP means 11 Multi-value conversion means 12 Descreening means 13 Color correction table 14 Color correction means 15 Error diffusion processing means D Binary image data (with dot information)
Do Multi-value converted image data (with halftone dot information)
Dd Descreened multi-value image data including intermediate values (no dot information)
Dc Color correction data Dx Color corrected multi-value image data (with halftone dot information)
Dz binarized image data such as error diffusion (with halftone dot information)

Claims (8)

A color output method for outputting a color halftone image by outputting a plurality of pixels using binary image data representing a halftone image,
De-screening the binary image data to convert it into multi-value image data;
Obtaining color correction data corresponding to the coordinate position of each pixel based on the multi-valued image data;
Converting the binary image data into color-corrected image data by performing color correction with color correction data corresponding to the coordinate position of each pixel;
Performing color output from the color-corrected image data;
A color output method consisting of The color output method according to claim 1, wherein color output is performed by performing error diffusion processing on the color-corrected image data. The color output method according to claim 1, wherein the color correction data is determined based on a color correction table prepared in advance according to an output device to be used. The color output method according to claim 3, wherein the color correction table is obtained by assigning color correction data to be added / subtracted to / from multi-valued image data representing a predetermined color. A color output method for outputting a color halftone image by a pixel output of a plurality of colors using binary image data D shaded by RIP processing,
Converting each value of the binary image data D from binary to multi-value to obtain first image data Do in which each pixel value is pseudo multi-value;
Descreening the first image data Do to convert the value of each pixel into second image data Dd having an intermediate value;
Referring to a color correction table prepared in advance, obtaining color correction data Dc corresponding to the second image data Dd for each coordinate position of each pixel;
Obtaining third image data Dx obtained by performing color correction by adding and subtracting the first image data Do and the color correction data Dc for each pixel coordinate position;
Converting the third image data Dx to error-diffused fourth image data Dz by performing error diffusion processing;
Outputting a color halftone image using the fourth image data Dz;
A color output method consisting of A color output device for outputting a color halftone image by pixel output of a plurality of colors using binary image data shaded by RIP processing,
Data processing means for performing color correction while maintaining the halftone dot information of the binary image data and converting it into multi-value image data;
Based on the color-corrected multi-value image data, output means for outputting a color image by outputting pixels that can take either binary values of drawing or non-drawing;
A color output device consisting of 7. The color output apparatus according to claim 6, wherein the data processing means generates intermediate multi-value image data having no halftone information from the binary image data. The data processing means converts each value of the binary image data from binary to multi-value, and obtains first image data in which the value of each pixel is pseudo-multi-value;
Descreening means for descreening the first image data and converting it to second image data in which the value of each pixel has an intermediate value;
A color correction table for obtaining color correction data for each coordinate position of each pixel based on the second image data;
Color correction means for adding and subtracting the first image data and the color correction data for each pixel coordinate position to obtain third image data subjected to color correction;
Furthermore, either the data processing means or the output means includes error diffusion processing means for converting the third image data into error-difference fourth image data by performing error diffusion processing. The color output device described.

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