JPH08185505A - Preparing method for color printing proof - Google Patents

Abstract

PURPOSE: To prepare a color printing proof with which moire or the like appearing on a high-resolution printed matter is reproduced with fidelity by a low-resolution color printer. CONSTITUTION: While referring to a threshold matrix 14, dot point area rate data ai, which are prepared from an image original 2 and contain three primary colors, for three editions at least are respectively converted to bit map data b1. Next, an area rate ci for every color is counted up while simultaneously referring to the bit map data b1 corresponding to the respective picture elements of a color printer 3 to output a color printing proof CPb. Afterwards, with the counted area rate ci as the weighting coefficient, three stimulus value data X, Y and Z of average color measured value data are calculated corresponding to color measured value data Xi, Yi and Zi for every color calculated in advance. Then, the calculates three stimulus value data X, Y and Z are defined as pixel data consisting of the input image data of the color printer 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention calibrates with a color printer that forms an image for each pixel by a density gradation method before producing a color printed matter with a halftone dot image by a color printing machine using a rotary press or the like. The present invention relates to a method of creating a color printing proof (also called a color printing proof) for printing.

[0002]

2. Description of the Related Art Conventionally, a color printing proof for proofing colors and the like has been produced by a color printer before producing a color printed product as a product by a color printing machine.

The use of a color printer to create a color printing proof is relatively inexpensive and inexpensive, and, as is well known, color printers are associated with color printers. This is because it is not necessary to make a plate-making film, a printing plate (PS plate), etc., and a hard copy having an image formed on a sheet can be easily made plural times in a short time.

FIG. 4 shows a flow of a conventional method for producing a color printing proof.

First, the image on the image original 2 is read by an image reading device such as a color scanner having a CCD area sensor or the like, and a gradation image for each color of R (red), G (green) and B (blue) is obtained. Data Ia is created (step S1:
Image reading process).

Next, the RGB gradation image data Ia is subjected to color conversion processing to obtain C (cyan), M (magenta), and Y.
It is converted into four-dot halftone dot area ratio data (also called halftone dot data) ai for each color (yellow) and K (black) (step S2). This conversion can be performed in various ways depending on the relationship with a color printing machine, which will be described later, and is usually the know-how of each printing company corresponding to the color printing machine.

The image created by this color printing machine is a halftone dot image. Therefore, when actually producing a color print, the halftone dot area ratio data ai after color conversion processing is expanded into bit map data. Although a plate-making film or the like is produced based on this, an automatic developing machine (automatic developing machine) or the like is required, and the steps after the plate-making film producing process are considerably complicated.

Therefore, in order to easily create a color printing proof, a color printer (hereinafter, also referred to as a color digital printer or DP) is used for the above-mentioned reason. The DP is a density gradation method, for example, digitally controls the light emission intensity and time of an LED (light emitting diode) or laser corresponding to three primary colors for each pixel to form an image on a donor film, and the image is formed on the image receiving sheet. The image is formed on the sheet by transferring the image onto a sheet, and is considerably cheaper than a color printing machine that prints using a PS plate prepared from the printing plate. Also,
Small volume and light weight.

Therefore, in order to use the DP, the halftone dot area ratio data ai of the 4th edition of CMYK created in step S2.
A so-called device (print, CRT, photograph, L
Image data (also referred to as common color space data) that does not depend on ED, for example, tristimulus value data X,
It is necessary to convert into Y and Z.

Therefore, image data processing for converting the halftone dot area ratio data ai of CMYK4 version into tristimulus value data X, Y and Z is performed (step S4). As this image data processing, processing using the Neugebauer equation has been conventionally used.

In this case, colorimetric value data Xi, Yi, Zi (i is 2 ⁴ colors = 16 colors in the case of the 4th edition of CMYK) for each color is previously measured by a colorimeter ( Step S
3). In this measurement, first, each color of 16 colors is printed in advance on a printing paper when a color printed matter is created by a color printing machine (usually called solid printing). The 16 colors specifically correspond to the presence or absence of each of C color, M color, Y color, and K color, and 2 ⁴ = 16 colors in total.

That is, the ground color W (white) of the printing paper when nothing is printed, the primary colors C, M and Y only, the color K (black), and the other colors C + M and C + Y. ,
C + K, M + Y, M + K, Y + K, C + M + Y, C + M
There are a total of 16 colors of + K, C + Y + K, M + Y + K, and C + M + Y + K. The reflected colors of these colors formed on the printing paper are measured by a colorimeter, for example, a spectrometer to obtain colorimetric value data Xi, Yi, Zi.

In the processing using the Neugebauer equation, the colorimetric value data Xi, Y are obtained as shown in the following equation (1).
The tristimulus value data X, Y, and Z are obtained by using the dot area ratio data ai as a weighting coefficient for i and Zi (step S
4).

X = Σai · Xi Y = Σai · Yi Z = Σai · Zi (1) The tristimulus value data X, Y, and Z thus obtained are supplied to the DP3. After converting the value data X, Y, and Z into data for each of the three primary colors of the LED based on a look-up table (LUT) (so-called device-dependent image data and also called unique color space data), the sheet is formed. A color printing proof CPa, which is a hard copy with an image formed on it, is created.

[0015]

However, as described above, when the tristimulus value data X, Y, and Z for DP3 are created by using the Neugebauer equation, the color printed matter created by the color printing machine is used. Since the color of the image formed on the color copy is measured with a colorimeter, it is possible to faithfully reproduce the color of the color print on the image on the hard copy, but on the color print. There is a problem that a peculiar pattern (hereinafter, also referred to as a false pattern) caused by interference fringes such as moire and rosette that appear cannot be reproduced in the image on the hard copy.

If these spurious patterns actually appear on the color printed matter, it is based on the request to faithfully reproduce the spurious patterns on the color printing proof Cpa. The color-printing proof CPa according to (1) can not be said in this respect, in general terms, to be an exact (fidelity) proof for color prints.

It is considered that the false pattern does not appear in the image on the hard copy of DP3 because the Neugebauer equation is an equation based on a kind of probability theory and therefore the false pattern cannot be reproduced.

The present invention has been made in view of the above problems, and faithfully reproduces a false pattern such as moire appearing on a high-resolution color printed matter by a relatively inexpensive and relatively low-resolution color printer. It is an object of the present invention to provide a method for producing a color printing proof that enables the above.

[0019]

According to the present invention, for example, as shown in FIG. 1, a color printer 3 for forming an image for each pixel on a sheet by a density gradation method based on pixel data forming input image data. In the method of creating a color printing proof using
A process of converting the halftone dot area ratio data ai for at least three plates into bitmap data bi by referring to the threshold matrix 14 for each of the halftone dot area ratio data ai including the primary colors, and Printer 3
Corresponding to each pixel, the bit map data bi for at least three plates are simultaneously referred to, and each color (the plate number is n
In the case of a plate, the process of counting the area ratio ci of each of 2 ⁿ colors) and the colorimetric value data X for each color that has been obtained in advance
i, Yi, Zi, and a step of calculating average colorimetric value data X, Y, Z using the enumerated area ratio ci as a weighting coefficient. It is characterized in that it is pixel data forming input image data.

Further, the present invention is characterized in that the dot area ratio data for at least three plates is the dot area ratio data of CMY3 colors or CMYK4 colors.

Furthermore, the present invention is characterized in that chromaticity value data for each color or density value data for each color is used instead of the colorimetric value data for each color.

Furthermore, the present invention is characterized in that the resolution of the color printer is lower than the resolution of the bitmap data.

[0023]

According to the present invention, a document created from an image original is
The threshold value matrix is referred to for each of the at least three halftone dot area ratio data including the primary color, and the halftone dot area ratio data is converted into bitmap data. Next, the bitmap data is simultaneously referred to for each pixel of the color printer that is to output the color printing proof, and the area ratio for each color is counted. Next, the averaged colorimetric value data is calculated by using the counted area ratio as a weighting coefficient for the colorimetric value data for each color obtained in advance. The calculated average colorimetric value data is used as pixel data forming the input image data of the color printer.

An image on a hard copy created by the color printer based on the pixel data created in this way,
That is, the color printing proof can reproduce not only the color matching with the color printed matter but also the false pattern appearing in the halftone dot image.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In the drawings referred to below,
Components corresponding to those shown in FIG. 4 are designated by the same reference numerals, and the description thereof will be omitted as appropriate.

FIG. 1 shows a general color printing system 11
The processing flow for creating the color print proof CPb according to this embodiment by the color digital printer (DP) 3 is shown for the color printed matter 12 created in (1).

First, the contents of the general color printing system 11 will be described.

In the general color printing system 11, the image on the image original 2 is read by an image reading device such as a color scanner having a CCD area sensor, and R
Gradation image data Ia for each color of (red), G (green), and B (blue) is created (step S1: image reading process). In this case, as the resolution of the CCD area sensor or the like, for example, about 400 DPI (dot per inch) is selected, and here, 1 dot (dot) corresponds to one pixel and has a density level of 256 or the like. It means a pixel according to the adjustment method.

Next, each pixel data forming the RGB gradation image data Ia is subjected to color conversion processing to obtain four plates for each color of C (cyan), M (magenta), Y (yellow) and K (black). Is converted into halftone dot area ratio data (also referred to as halftone dot data) ai (step S2: color conversion process). Since this conversion can be performed in various ways depending on the relationship with a color printing machine, which will be described later, it is usually the know-how of each printing company corresponding to the color printing machine. Note that UCR (under-color re
Moval) processing is not performed, the RGB gradation image data Ia is converted into halftone dot area ratio data ai of C, M, and Y plates. In addition, if, for example, the Y color does not exist on the color printed matter 12, it is needless to say that it may be converted into the halftone dot area ratio data ai of C and M.

Next, CMYK4 created in pixel units
The resolution is 200 for the halftone dot area ratio data ai
About 0 DPI (here, 16 to facilitate understanding)
00DPI. ) Refer to four threshold value matrices (also called threshold value templates) 14 having a predetermined halftone angle for each of the CMYK4 planes, and each threshold value in each element of the threshold value matrix 14 and the value of the halftone dot area ratio data ai Are compared with each other to be converted into binary data having a value “0” or a value “1”, that is, bitmap data bi (step S5: comparison process). Note that, normally, the halftone angle has an angle difference of, for example, 15 ° between the threshold matrix 14 for the C plate and the threshold matrix 14 for the M plate, and in practice, the halftone angle is, for example, CMYK. In the 4th edition, the C edition has an angle difference of 15 °, 45 °, 75 °, etc. with respect to the reference (0 °).

FIG. 2 is a diagram schematically illustrating the threshold matrix 14 and the like in order to explain the comparison process (bitmap expansion process) in step S5 in detail.

In FIG. 2, the two diagrams drawn in the uppermost row show that one dot of the 400 DPI halftone dot area ratio data ai is converted into 16 dots of the 1600 DPI bitmap data bi.

For example, one dot of the halftone dot area ratio data ai is the C plate, and the halftone dot area ratio data ai is ai = 3.
If it is 0%, this and the threshold matrix 14 for C version are referred to. The threshold matrix 14 is, for example,
Threshold values T as shown in FIG. 2 are spirally arranged in the elements of the matrix. The threshold T drawn in the element in this example is
It is selected to be an integer multiple of the value obtained by dividing 100% by the number of elements 17 (16 + 1). The step does not have to be an integral multiple.

As is well known, the expansion into the bit map data bi, that is, conversion into binary data, is performed by the following equation (2),
This is performed as shown in equation (3).

Ai ≧ T → 1 (2) ai <T → 0 (3) Thus, one pixel of the C plate shown at the bottom of FIG. 2 (halftone dot area ratio data ai = 30%) Bitmap data bi for each pixel) is created. As described above, with respect to the threshold matrix 14 for C plate, M, Y,
The threshold matrix 14 for K plate has a predetermined selectable halftone angle. Further, in this example, an irrational number network is used as the threshold matrix 14, but it goes without saying that a rational number network may be used.

Next, on the basis of the bit map data bi created in this way, processing by a phototypesetting machine, an automatic developing machine, etc. is performed (step S6: plate making process), and the 4th plate having a halftone image as a block copy. A plate-making film 16 and a PS plate 17 as a printing plate are prepared.

Finally, the PS plate 17 is used to prepare a color printed matter 12 formed with a halftone image by a color printing machine having a rotary press or the like (step S7: printing process).

The halftone image on the color printed matter 12 includes
False patterns such as moire and rosette appearing due to the use of the threshold matrix 14 having different halftone angles.

The above is the general color printing system 11
The following is a description of the configuration of an embodiment according to the main part of the present invention. In this embodiment, a data processing step S11 according to the main part of the present invention is provided.

In this embodiment, the resolution of DP3 is 400 DPI for easy understanding. Assuming this, 16 dots of the bitmap data bi correspond to 1 dot of DP3, that is, 1 pixel.

FIGS. 3A and 3B show examples of bitmap data bi for the C and M versions corresponding to one pixel of DP3, respectively. It is assumed that each element of the remaining Y-version and K-version bitmap data bi has the value “0”. The C version bitmap data bi is the same as that shown in FIG.

Therefore, for each pixel of DP3, CMY
The K4 version of the bitmap data bi (it goes without saying that the C version and the M version of the two versions of the bitmap data bi are sufficient) is referred to at the same time, and each color (the version number is 4 enumerating 2 ^4-color area ratio ci of each per color) of the process is performed because it is (step S12: enumeration process). FIG.
In the pixels of A and FIG. 3B, the area ratio ci for each color is calculated as follows.

C color: ci = c _C = 3/16 (When the C plate and the M plate are overlapped and seen transparently, the area where C and M colors overlap is C + M = B area ratio. and c _{C + M)} C _{+ M color:. c C + M = 2} /16 W _{color: c W = 11/16 (} C plate and when viewed transparently overlaid the M plate, C-color and M-color The area ratio ci of the remaining colors (13 colors such as Y color and K color) has a zero value.

Next, the processing of step S3 described in detail in the section of the prior art (1 printed on the color printed matter 12)
Colorimetric value data Xi, Yi, Zi for each color measured in advance by the process of measuring 6 solid colors with a colorimeter)
(I is 2 ⁴ colors = 16 colors in case of CMYK 4th edition)
With respect to the area ratio ci for each color counted in step S12
Is used as a weighting factor to obtain tristimulus value data X, Y, and Z, which are average colorimetric value data, as shown in equation (4) (step S13). In other words, the colorimetric value data Xi, Yi, Z
New tristimulus value data X, Y, and Z are obtained by weighted averaging i with the area ratio ci for each color.

X = Σci · Xi = (3/16) X _C + (2/16) X _{C + M} + (11/16) X _W Y = Σci · Yi = (3/16) Y _C + (2 / 16) Y _{C + M} + (11/16) Y _W Z = Σci · Zi = (3/16) Z _C + (2/16) Z _{C + M} + (11/16) Z _W (4) The new tristimulus value data X created in this way,
Y and Z are supplied to DP3, and this new 3
The stimulus value data X, Y, Z, in other words, the common color space data is converted into pixel data for each of the three primary colors of the LEDs and the like, in other words, converted into unique color space data by a look-up table (LUT) or the like, and then the sheet. A color print proof CPb, which is a hard copy with an image formed on it, is created. The LUT, which is a conversion unit (conversion table) for converting the common color space data into the unique color space data, is DP3.
It goes without saying that it may be placed outside the.

On the color printing proof CPb thus created, the false patterns such as moire and rosette which are almost the same as those appearing on the color printed matter 12 are faithfully reproduced.

In this case, the resolution of DP3 is 400 DPI.
2000D even though it is a relatively low value
It is possible to reproduce on the color printing proof CPb false patterns such as moire and rosette that are almost the same as those appearing on the color printed matter 12 created by the color printing machine having the resolution of PI.

In other words, the color printing proof CPb which faithfully reproduces the false pattern appearing on the color printed matter 12 can be produced at a low cost with a simple structure. As for color reproducibility, since the colorimetric value data Xi, Yi, and Zi are used, the color on the color printed matter 12 can be faithfully reproduced.

In the above-described embodiment, the tristimulus value data X, Y, and Zi are calculated using the colorimetric value data Xi, Yi, and Zi.
Although Z is created, the chromaticity value data, the density value data, or the like may be used instead of this to create the average colorimetric value data. In short, the average colorimetric value data on the common color space may be created using the data measured on the device-independent color space (common color space).

Further, as the arrangement of the threshold matrix 14, even when a so-called FM screen in which the arrangement of halftone dots is random is used, the present invention can be applied to produce a color printing proof.

In practice, DP3 is calculated using the Neugebauer equation.
(As DP3, a model "Pictrography 3000" manufactured by Fuji Photo Film Co., Ltd. was used.) An image on a color printing proof CPb and an image on a printing paper actually created by using a color printing machine. , A color printing proof C actually created by DP3 based on this embodiment
When compared with the image on Pb, D based on the example
In the image on the color printing proof CPb actually created in P3, it is possible to faithfully reproduce the false patterns such as moire and rosette appearing on the image on the printing paper created by using the color printing machine, and also for the feeling of roughness and jump. It was possible to create an image having a feeling closer to the image on the printing paper created by the color printing machine as compared with the image created by DP3 using the Neugebauer equation. Note that the number of screen lines of the color printed matter at the time of this comparison is 175 lines, and CMYK
The mesh angle of the 4th plate is 0 °, 15 °, 45 as described above.
And 75 °.

The present invention is not limited to the above embodiment,
It goes without saying that various configurations can be adopted without departing from the gist of the present invention.

[0053]

As described above, according to the present invention, when the pixel data forming the input image data for the color printer is created, the Neugebauer equation is not used and the bitmap data is used. Created from a different perspective.

The pixel data created in this manner was supplied to a color printer, and a false pattern such as moiré or rosette peculiar to a color printed matter could be accurately and faithfully reproduced on a color printing proof output from this color printer. .

Here, what is described as a completely new viewpoint is that it is conventionally believed that a low-resolution color printer of, for example, about 400 DPI cannot reproduce a false pattern of a color printed matter of, for example, about 2000 DPI. From the viewpoint of how to reproduce this on a low resolution color printer, as a result,
Based on a completely new configuration (concept) of counting the area ratio of each color corresponding to the pixels of the color printer using bitmap data and calculating the average colorimetric value data using this as the weighting factor of the colorimetric data. Because there is.

The reason why the false pattern appears according to the present invention will be described below. The false pattern is generated by using a threshold matrix having different halftone angles for each of the halftone dot area ratio data for at least three plates including the three primary colors. Potentially when expanded to map data. Therefore, it is possible to reproduce the false pattern by reproducing the color printing proof with a color printer having a pixel row with a period shorter than the period of this potentially occurring false pattern.

[Brief description of drawings]

FIG. 1 is a flow chart including a processing flow of an embodiment of the present invention and used as a whole for explaining a process of creating a color printing proof corresponding to a color printed matter.

FIG. 2 is a diagram used for explaining creation of bitmap data in the processing flow of FIG.

FIG. 3 is a diagram used for explaining a process of calculating an area ratio in the processing flow of FIG. 1, and FIG. 3A is a diagram used for explaining bitmap data of one pixel for C plate; FIG. 3b shows M
FIG. 4 is a diagram used for explaining bit map data of one pixel for plate.

FIG. 4 is a flowchart provided for explaining a conventional technique.

[Explanation of symbols]

2 ... Image original 3 ... Color digital printer 12 ... Color printed matter 14 ... Threshold matrix ai ... Halftone dot area ratio data bi ... Bitmap data ci ... Area ratio CPb ... Color printing proof

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication H04N 1/405 H04N 1/40 104

Claims (4)

[Claims] 1. A method of creating a color print proof using a color printer which forms an image for each pixel on a sheet by a density gradation method based on pixel data forming input image data, and is created from an image original, A step of converting the halftone dot area ratio data for at least three plates into bitmap data by referring to a threshold matrix for each of the halftone dot area data for at least three plates including three primary colors; Corresponding to each pixel of, at the same time, referring to the bit map data for at least three plates, counting the area ratio for each color (each 2 ⁿ colors when the plate number is n plates), A step of calculating average colorimetric value data using the enumerated area ratio as a weighting coefficient for the colorimetric value data obtained for each color in advance; Color proof creation method characterized by the value data, the pixel data constituting the input image data. 2. The method for producing a color printing proof according to claim 1, wherein the halftone dot area ratio data for at least three plates is halftone dot area ratio data of three colors of CMY and four colors of CMYK. 3. A color printing proof according to claim 1, wherein chromaticity value data for each color or density value data for each color is used instead of the colorimetric value data for each color. Method. 4. The method for producing a color printing proof according to claim 1, wherein the resolution of the color printer is lower than the resolution of the bitmap data.