JP3538361B2 - Method of setting halftone dot area ratio (c, m, y, bk) of each color plate for producing a four-color halftone print image excellent in color reproduction of color original - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a color halftone print image having excellent color reproduction of a color original. More specifically, the present invention provides a continuous tone
The present invention relates to a novel color halftone print image production method capable of reproducing a color (color) of a color original of (e) as a halftone color halftone print image.

More specifically, the present invention relates to a continuous tone (cont)
color (color) of the color original of inuous tone)
When reproducing as a halftone color halftone print image, (1). Dot gain which is extremely important in guaranteeing color consistency (color consistency) , Optical and physical halftone dot thickening), that is, the problem of the correction process of the dot gain (DG) effect is rationally quantified and solved, and (2). A gradation conversion process (which may be referred to as a gradation proportional compression process in the present invention) which is a very important elemental technology in color reproduction by multicolor printing of the M and Y plates and the black plate (BK plate). ), Gray balance processing, inking processing, and masking (color correction) processing are quantified reasonably, so that color matching (color consistency) is highly assured. It is intended to provide a manufacturing method.

Further, the present invention employs a method of quantifying and processing all of the above-mentioned important processing techniques (color reproduction techniques) when producing a color halftone print image as described above. Therefore, it is an object of the present invention to provide a new method capable of producing a high-quality color halftone print image under automation and skimming.

[0004]

2. Description of the Related Art Conventionally, continuous tone color film originals (color transparent originals, transparenc)
In order to produce a halftone color halftone print image from a color document such as y), the color document is color-separated to produce each color plate (C, M, Y, BK plate). Color plate making)
This is done by overprinting each color plate.

[0005] The color separation means that R, G,
B-system image information is taken in, and C, M,
This is to receive Y-system image information. And the C,
A color plate for color printing (C, M,
Y version) is produced. In color printing, C,
From the viewpoints of reducing the amounts of M and Y inks used and enhancing the tone (color tone and density gradation) of a printed image, black plates (BK plates) are generally used. In other words, in color printing, the black plate (BK plate) is extremely important. In the present invention, the concept of a color plate includes:
In view of the importance of the black plate (BK plate), in addition to the C, M, and Y plates for so-called C, M, and Y inks, the black plate (BK plate) for black ink is included. Should be interpreted as:

As described above, each color plate (C,
(M, Y, BK) in order to produce color halftone prints, the color reproducibility (color repr
In other words, from the viewpoint of reproducing the color (color) of a color original with high degree of matching (color matching) on a printed image from the viewpoint of (1). A halftone dot of a predetermined pixel (which has a predetermined size, that is, a halftone dot area ratio and a halftone dot area percentage value) set on the printing plate of each color plate by the separation is inevitably thickened in the printing process. There is a phenomenon (which will be described in detail later, which is called a dot gain phenomenon in the art), and it is difficult to quantify the dot thickening phenomenon. In addition to the fact that color consistency cannot be guaranteed in advance, and (2) it is difficult to quantitatively grasp the dot gain phenomenon (thickening phenomenon of halftone dots) described above, Color version (C, M, Y version) and black version (B In order to guarantee color matching by overprinting of the K plate), the halftone dot area ratio (bk) of the black plate (BK plate), which is an important printing plate in color printing, and the dot area ratio (bk) of each color plate (C, M, Y plate) Since it is difficult to quantitatively grasp the mutual relationship between the halftone dot area ratios (c, m, y), color matching cannot be guaranteed in advance in the plate making design stage.

As can be seen from the above (2), in the prior art, in a multicolor plate making (C, M, Y, BK plate) using a predetermined black plate (BK plate), it is necessary to guarantee color matching. The problem of defining the interrelationship between the BK plate and each color plate (C, M, Y plate) has not been solved. In other words, the halftone dot area ratio (bk) of the predetermined black plate (BK plate) The problem of defining the quantitative relationship between the halftone dot area ratios (c, m, y) of the respective color plates (C, M, Y plates) has not been solved. In addition, the process of under color addition (UCA) (Under Color Addition) and under color removal (UCR) (Under Color Removal) by the black plate (BK plate), which is generally performed in the industry, is rationally and quantitatively performed. The problem to be determined has not been solved.

Further, other important problems in producing a color matching color halftone print image include: a gradation conversion for converting a continuous gradation color original such as a color film original into a halftone gradation; (Gradation proportional compression) technology ・ Maintains the gray balance of printing inks (C, M, Y inks) to achieve high quality color reproduction in the world of halftones with gradation conversion A masking (color correction) technique for correcting color impureness due to an improper absorption of a printing ink (C, M, Y ink) to be used in a halftone converted gray scale world;・ Gain (DG) is optical
This is called a dot gain (ODG). In addition to the correction of the ODG effect, the correction of the dot thickening phenomenon on a printing press, the so-called mechanical dot gain (M
DG) effect correction technology, etc., and these are all color plates (C, M, Y, BK).
This is related to the size (dot area ratio) of the halftone dot of the (version), and there is a problem of how to quantitatively quantify it.

However, in the prior art, regarding the important elemental technologies for guaranteeing the high-quality color consistency (color consistency) described above, these elemental technologies are organically and quantitatively centered on halftone dots. There is no plate making or printing technology that can produce high quality four-color (C, M, Y, BK) color halftone prints.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned limitations of the prior art. That is, the present invention relates to a method for producing a four-color halftone print image of halftone gradation excellent in reproducibility of color (color) and color tone of a continuous tone color original, and includes a dot gain (DG) and a UCR. A method of producing a four-color halftone print image with a new halftone gradation, which can quantify such problems rationally and pre-plan the reproducibility of the colors (colors) and color tones held in the color original It is about.

According to the present invention, when a color halftone print image of halftone is produced by multi-color plate making (four plates of C, M, Y, and BK), for example, the continuation of a color original which is the core In a tone conversion operation for converting a tone into a halftone dot tone, when setting a tone conversion curve (tone curve) that defines the tone conversion, the above-described problem of dot gain (DG) in the art. Incorporating (weaving) means to comprehensively solve the problems of UCR and UCR, color matching (color co
The gradation conversion curve (tone curve) that guarantees the nsistency is set. In other words,
The present invention relates to each color plate (C, M,
(C, m, y, bk) of the Y, BK version). The problem of dot gain (DG) and UC for ensuring the above-mentioned advanced color matching
An approach integrating solutions to the problem of R and the like is first proposed by the present invention.

[0012]

SUMMARY OF THE INVENTION In general, the present invention utilizes the R, G, B system image information (xc, xM, xY) of each pixel of a color original, and (i) (Ii) A predetermined amount of the gray (black) component of the R, G, B system pixel information equally absorbed in each pixel is determined by a black plate (BK plate)
(Iii) masking processing for adjusting the improper absorption of printing ink based on the correction amount of the dot gain (DG) effect and the amount of the inking processing.
Each color plate (C, M, and C) capable of producing a C, M, and Y four-color halftone print image excellent in color reproduction of a color original.
In the method of setting the dot area ratio (c, m, y, bk) of (Y, BK version), (i) the proportional compression processing of the gradation is performed by the following formulas (100) to (102). R, G,
The halftone dot area ratio (c1, m1, y1) of each color plane of the C, M, and Y systems is obtained from the image information (xc, xM, xY) of the B system, and (ii). (ii) -1. The predetermined amount of the gray (black) component of the R, G, B image information equally absorbed in each pixel is determined by a dot area ratio (bk) obtained by a predetermined black plate function set in advance. ) And (ii) -2. Halftone dot area ratio (c2, C3, M, Y) after inking.
m2, y2) is determined by the following expressions (103) to (105). (iii) The masking process is performed by the given black plate (BK) by the following expressions (106) to (108).
Plate area ratio (bk) and the above (c2, m2, y2)
Is used to determine (c3, m3, y3),
(iv). Color reproducibility of a color document characterized by using (c3, m3, y3) and a given (bk) as a final dot area ratio (c, m, y, bk). Excellent C,
A method for setting a dot area ratio (c, m, y, bk) of each color plate (C, M, Y, BK plate) capable of producing a four-color M, Y, BK halftone print image .

[0013] 1. Formulas (100) to (102): c1 = AHc + [(1−10− ^{γ · xc} ) / (1−10− ^γ )] · (Asc−AHc) (100) m1 = AHM + [(1-10− ^{γ · xM} ) / (1-10− ^γ )] · (AsM−AHM) (101) y1 = AHY + [(1-10− ^{γ · xY} ) / ( 1-10- ^γ )] · (AsY−AHY) (102)

However, the symbols in the formulas (100) to (102) mean the following. The expression (10
0), and the other color plates (M, Y) will not be described because of similarity. 1) c1: Halftone dot area ratio at an arbitrary pixel point of the C plane image. 2) xc: Image information obtained through an R filter of a color original. Note that xM and xY are a G filter and a B filter, respectively.
5 shows image information obtained through a filter. 3) AHc: The halftone dot area ratio set in the H portion (lightest portion) of the C-plate image. 4) Asc: The dot area ratio set in the S portion (darkest portion) of the C-plate image. 5) γ: any coefficient including Dsc / nc. However, Ds
c is a solid density value of the C-plate image, and nc is a Yule-Nielsen coefficient, and these are R filter light reflectance (R
c) and the relational expression (Yule-Nielsen equation) R of the dot area ratio (c)
c = (1−c + c · 10− ^{Dsc / nc} ) ^nc is established.

[0015] 2. Formulas (103) to (105):   c2 = (c1-bk) / (1-bk) (103)   m2 = (m1-bk) / (1-bk) (104)   y2 = (y1-bk) / (1-bk) (105)

[0016] 3. Formulas (106) to (108):   1-c2 + c2.Rsc-kc.c2 (1-c2)     = [1-c3 + c3.Rsc-kc. (C3 + bk-c3.bk)       (1-c3) (1-bk)] · (1-m3 + m3 · RsM)       · (1-y3 + y3 · RsY) · (1-bk + bk · RsBK)                                                   ............ (106)   1−m2 + m2 · GsM−km · m2 (1-m2)     = (1-c3 + c3.Gsc). [1-m3 + m3.GsM-kM.       (M3 + bk-m3 · bk) (1-m3) (1-bk)]       · (1-y2 + y2 · GsY) · (1-bk + bk · GsBK)                                                   ............ (107)   1−y2 + y2 · BsY−kY · y2 (1-y2)     = (1-c3 + c3 · Bsc) · (1-m3 + m3 · BsM)       [[1-y3 + y3.BsY-ky] (y3 + bk-y3.bk)       (1-y3) (1-bk)] · (1-bk + bk · BsBK)                                                   ............ (108)

However, the meaning of each symbol in the expressions (106) to (108) and the operation of the expression are as follows. The description of symbols having similarity is omitted. 1) kc: a correction coefficient of c1 (1-c1), which is an ODG correction function (quadratic expression) for correcting an optical dot gain (ODG) effect in a C-color monochrome image. 2) Rsc, RsM, RsY, RsBK: C, M, Y, B
Each R filter light reflectance of K solid print. 3) Gsc, GsM, GsY, GsBK: C, M, Y, B
Each G filter light reflectance of K solid print. 4) Bsc, BsM, BsY, BsBK: C, M, Y, B
Each B filter light reflectance of the K solid print. 5) In the equation (106), c3 is obtained using m2 and y2 as the unknowns m3 and y3. 6) In equation (107), c obtained from equation (106)
3, and using the above y2 as the unknown y3, m
Ask for 3. 7) In equation (108), c obtained from equation (106)
3, and y3 is obtained using m3 obtained from Expression (107).

Further, the present invention provides the above-mentioned “formula (100)-
(102) ", the conditions for reproducing high-quality colors (colors) between the color plates (C, M, Y plates), ie,
The condition for maintaining the gray balance is adopted. In the present invention, each color plate (C, M,
The condition for maintaining the gray balance of the (Y version) is as follows:
0-1) to (102-1). xc = xc '... (100-1) xM = (Dsc / DsM) .multidot.M'... (101-1) xY = (Dsc / DsY) ) · XY ′ (102-1) However, in the expressions (100-1) to (102-1),
(Xc ′, xM ′, xY ′) are R, G, B-based pixel information (xc, xM, xY) before gray balance processing, respectively.
Is shown.

Still further, the present invention provides a method for compensating for a mechanical dot gain (MDG) effect on a printing press.
The halftone dot area ratio (c, m, c) for each color plate (C, M, Y, BK)
As (y, bk), numerical values determined by the following equations (109) to (112) are adopted. c ′ = c3-MDc · c3 (1-c3) (109) m ′ = m3-MDM · m3 (1-m3) (110) y ′ = y3-MDY · y3 (1) −y3) (111) bk ′ = bk−MDBK · bk (1−bk) (112) Note that MDc, MDM, MDY, and MDBK are each color for correcting the MDG effect. The coefficients of the correction functions (quadratic equations) of the plates (C, M, Y, and BK plates) are shown.

Hereinafter, the technical configuration of the present invention will be described in detail with reference to the drawings. It goes without saying that the present invention is not limited to the illustrated one.

It goes without saying that the color reproduction of a color original image by printing is performed by using printing inks (C, M, Y, BK inks). How to determine the halftone dots of a predetermined size to be printed (applied) rationally. In color printing, various papers (printing papers) and inks (process inks) are used.
Needless to say, the color development (color appearance) differs depending on the combination. For this reason, in order to produce a color print having a desired quality reasonably and efficiently, there is a strong demand for a technique capable of accurately predicting color reproducibility (print color) before printing. ing.

A conventional technique for predicting the "color" of a color halftone print will be described below.

As is well known, most color print images are produced by printing color plates of four colors (C, M, Y, and BK), and each color plate (printing plate) image has various colors. It consists of halftone dots of size. These color images are sequentially printed on white paper (print paper) by a printing machine to reproduce (color) the colors.

Conventionally, Neugebauer's equation is generally employed for predicting the "color" of a color halftone print. Ne
The equation of ugebauer expresses each color (C, M,
(Y, BK) is used as a variable to express “print color”. Hereinafter, in order to help understanding of the present invention,
The theoretical formula of the above-mentioned Neugebaure formula and another theoretical formula regarding color reproduction will be described in detail.

The Neugebauer equation used to predict the "color" of a color halftone print is of the paper and ink separated form as shown below. Now, when the four-color printout is viewed through an R (red) filter, its light reflectance (hereinafter referred to as R filter light reflectance or simply light reflectance) (R) is expressed as follows. R = Rp ((1-c) (1-m) (1-y) (1-bk) + c (1-m) (1-y) (1-bk) Rsc + (1-c) m ( 1-y) (1-bk) Rsm + (1-c) (1-m) y (1-bk) Rsy + (1-c) (1-m) (1-y) bkRsbk + cm (1- y) (1-bk) Rscm + c (1-m) y (1-bk) Rscy + c (1-m) (1-y) bkRscbk + (1-c) my (1-bk) Rsmy + ( 1-c) m (1 -y) bkRsmbk + (1-c) (1-m) ybkRsybk + cmy (1-bk) Rscmy + cm (1-y) bkRscmbk + c (1 -m) ybkRscybk + (1 -c) mybkRsmybk + cmybkRscmybk] ……………………… (1)

In the above equation (1), each symbol means the following. That is, (1) R = R filter light reflectance when a color halftone print printed in four-color printing is viewed through an R filter, (2) Rp = light reflectance of paper, (3) c, m, y, bk = each color (4) Rsc = the light reflectance of paper measured by the R filter of the printed C-ink solid portion to 1 (5) Rs
cm = reflectance when the light reflectance of the paper measured by the R filter of the solid portion where the printed C and M are overprinted is set to 1, (6)
Rscmy = R of the printed solid portion of C, M and Y
The reflectance when the light reflectance of the paper measured by the filter is set to 1, (7) Rscmybk = the light of the paper measured by the R filter of the printed solid portion of C, M, Y and BK Reflectance of 1
Represents the reflectance when

Further, G of the four-color printing color dot printing product
(Green) Light reflectance through filter (G) and B
The light reflectance (B) through the (blue) filter is expressed in the same manner as in the above equation (1). The relational expression of the light reflectance for the G light and the B light is of a type in which the symbol R is replaced with the symbols G and B in the above-mentioned expression (1), and therefore, the details of these two expressions are omitted. .

As described above, Neugebauer's equation (1) is an extremely complicated theoretical equation, and it is difficult to find a solution. Pollak, on the other hand, worked to establish a method to find a practical solution. ・ Regarding the light density (optical density) of the overprint of solid ink, each color separation (R light, G light, B light) Assuming that the addition rule of light density is satisfied, the light reflectance of the overprint of the solid ink is the light reflectance of each color separation. Assuming that this is expressed by the product, Neugebauer's (1)
It has been shown that the equation can be factored into four terms.

The Pollak equation of the R filter light reflectance (R) of the color halftone print image including the BK plate (black plate) term using the above assumption is expressed by the following formula (2). Is what is done. R = Rp (1-c + cRsc) (1-m + mRsm) (1-y + yRsy) (1-bk + bkRsbk) (2) Note that the same formulas are also applied to the light reflectance of G light and B light. In these formulas, R in the formula (2) is replaced by G and B, respectively. When the black version (BK version) is not used, the Pollak equation (2) is a formula excluding the bk term. For example, it can be used when considering masking (color correction) for correcting improper absorption of ink. Such use of the Pollak equation is being employed in the present invention as described below.

As described above, the theoretical expression for expressing the “print color” in a color halftone print is the above-mentioned Neug
Ebauer's equation (1) and Pollak's equation (2) are known, but the latter expresses the simplicity of the equation and each term in the equation represents paper and the ink film layer of each of the four colors. That is, it is evaluated as excellent because the structure of the printed matter is well expressed.

By the way, in the Pollak equation (2), each term represents a light in a single-color image when the light reflectance of paper is set to "1", for example, a single-color image printed with only C ink (C print). This corresponds to the Murray-Davies equation representing the relationship between the reflectance (R) and the dot area ratio (c). Now, taking the R filter light reflectance (R) of the C print as an example, the Murray-Davies equation is expressed by the following equation. R = (1−c + cRsc) = (1−c + c10− ^Dsc ) (3) (Note) In the above equation (3), Rsc is a solid (s) of the C print.
olid) indicates the R filter light reflectance, and Rsc = 10 ^−Dsc
Is defined. Note that this definition formula is expressed by a concentration formula, D
= Log can be easily understood from Io / I. That is, D = Dsc = -log Io / I = -logRsc, and therefore R
sc = 10 ^-Dsc

As described above, various expressions have been described as expressions for expressing "printing color" in color halftone prints. For example, Pollak's expression (2) or Malle-Davies
The light density (theoretical value) calculated by equation (3) does not match the actual printed matter density (actually measured value). The cause of this discrepancy is:
As is well known, "dot gai
n) "(DG). There are two types of dot gain (DG) described above. One of them is a printing plate (for example, a positive film) in a printing process for producing a printed matter. This is because the printing ink transferred onto the printing paper via the halftone dots becomes thicker and the area ratio of the halftone dots becomes larger.・ Dot gain (mechanical
dot gain) ”(MDG), and the amount of dot thickening varies depending on the printing press and printing conditions.
Can be quantitatively evaluated if the printing conditions are stable.

On the other hand, the dot thickness (dot gain) (D
G) includes the above “mechanical dot gain”
In addition to (MDG), when the incident light incident on the halftone dot and the printing paper around the halftone dot reaches the human eye and is recognized as the light density, the exact size (area ratio) as expected. Even if the halftone dot is printed, there is a phenomenon that the halftone dot becomes thicker from an optical viewpoint. The incident light that has entered the halftone dot and the surrounding printing paper is not reflected 100% as it is and reaches the eyes, but is referred to as a halftone dot → the surrounding printing paper, a printing paper surrounding the halftone dot → the halftone dot, and the like. There are optical paths, all of which result in changes in light density. That is, in an actual printed matter, even if a halftone dot having an accurate size (area ratio) is printed as expected, the same effect as when the halftone dot is apparently fat due to the above-described optical cause is obtained. Occurs.

In order to quantitatively understand the above-mentioned halftone dot thickening phenomenon, the above-mentioned equation (3) of Murray-Davies may be used. That is, the light density calculated by putting the area ratio of the halftone dots in a fat state during printing into the Murray-Davies equation (3) indicates a value lower than the actually measured light density of the printed matter.
The change in light density from the above-mentioned optical point of view produces the same effect as the apparent increase of the halftone dots of the printed matter. The amount of halftone dot thickening based on the above optical point of view is referred to as “optical dot gain”.
l dot gain) ”(ODG).
In the present invention, the above-mentioned dot thickening phenomenon is referred to as a dot gain (DG) effect or an optical dot.
It is called a gain effect (ODG) effect or the like.

As will be described later, the present invention accurately predicts color reproducibility (printing color) by rationally correcting the above-mentioned DG (dot gain) at a stage before printing. Method of producing color halftone prints, especially the gradation from continuous tone color original images to halftone color halftone print images in which the core DG (dot gain) effect is rationally corrected. It seeks to provide a conversion method. In the present invention, the correction of the DG (dot gain) effect is primarily for correcting the thickening of halftone dots due to ODG, which is difficult to quantitatively evaluate from the viewpoint of color (color) reproducibility. However, thickening of halftone dots by MDG, which is relatively easy to quantitatively evaluate based on printing conditions, may be incorporated into the correction target. In other words, the present invention provides a total DG (dot / dot) of the ODG effect and the MDG effect.
Gain) effect is subject to correction and color reproducibility (printing color)
It is intended to provide a technical means for accurately controlling the data.

Here, the conventionally proposed OD
The G effect correction means will be described. From the viewpoint of correcting the ODG effect, the Murray-Davies
Equation (3) has a limit. In this regard, Yule-N
ielsen introduced the coefficient (n) in order to improve the defect of the difference (mismatch) between the light density (theoretical value) calculated by the above Murray-Davies formula (3) and the actual print density (actual value). A correction formula is proposed. This Yule-Nielsen equation is
For example, taking the R filter light reflectance (Rc) of a C ink print (monochromatic image) as an example, it is represented by the following equation (4). Rc = (1−c + c10− ^{Dsc / n} ) ⁿ (4) In the Yule-Neisen equation (4), the n value is theoretically derived when 1 or 2. However, in other cases, it is a value determined so as to match the actually measured value of the density. Although described in detail later, the aforementioned Yule-Nie
The lsen coefficient (n) is also used in the DG effect correction means of the present invention. In other words, the D of the present invention
The means for correcting the G effect is intended to make the correction of the DG effect more accurate while utilizing the coefficient (n) which is a result of Yule-Neilsen.

Hereinafter, the present invention provides a theoretical formula (color reproduction formula) for expressing the "printed color" of a printed material using the dot area ratio (c, y, m, bk) of the C / M / Y / BK plate as a variable. In the establishment, a more advanced DG (dot gain) correction means adopted by the present invention, in particular, an ODG (optical dot
The correction term (the theoretical formula for correcting the DG effect) introduced to rationally solve the problem of (gain) will be described in detail.

FIG. 1 shows a DG image of a general printed matter (a halftone printed image produced using a positive film printing plate).
It is a contour map of (MDG + ODG). FIG. 1 shows the DG phenomenon observed under various screen rulings (65 lines, 150 lines, etc.), and shows that the DG is maximized in a halftone area (a halftone dot area of 50%). ing.

ODG (optical dot gain)
Also shows a curve similar to FIG. That is, when the ODG effect is expressed by light reflectance, the highlight (the brightest part, Highligh
t part. Hereinafter, it may be abbreviated as H. ) To shadow (darkest part, shadow part; hereafter abbreviated as S) (dynamic range)
It shows the largest value at the middle gradation (Midtone, hereafter sometimes abbreviated as M), and shows the smaller value as the halftone dot area ratio increases or phenomenon occurs from there. The ODG curve is obtained by plotting the light reflectance or (optical) density value of the color document on the horizontal axis and the dot gain amount on the vertical axis to plot the relationship between the two.

The present invention relates to an OD curve represented by the ODG curve.
In order to quantitatively evaluate and quantitatively correct the G effect (thickening phenomenon of halftone dots), the following important preconditions are adopted. It goes without saying that adoption of such preconditions has not been proposed to date. That is, the present invention provides:-the ODG curve can be approximated by a quadratic equation, that is, a quadratic equation is useful as a correction function in the correction processing of the ODG effect; The following condition is adopted: the height of the following equation, that is, the height of the portion corresponding to the halftone (M) can be defined by multiplying by a predetermined correction coefficient. Although described in detail later, in the present invention, a quadratic equation represented by f (a) = ka (1-a) is adopted as a correction function for correcting the ODG effect. In the correction function f (a), a represents a halftone dot area ratio (synonymous with the halftone dot area ratio) of each color plate, and k represents a correction coefficient. The correction coefficient k is expressed as kc, km, or kY, especially when it indicates that it is related to each color plate (C, M, Y plate).

As described above, Yule-Nielsen solves the drawback of Murray-Davies' equation (3) for predicting the density value (actual measurement value) of an actual printed matter, that is, the difference between the theoretical value and the actual measurement value. Equation (4) in which the coefficient (n) is introduced into the equation (4) is proposed. In this connection, a description will be given below of a means for correcting the ODG effect having the above-described correction function (quadratic equation) as a core employed by the present invention.

Assuming that the halftone dot area ratio of a desired pixel, that is, the halftone dot area ratio per unit area is "a", the light reflection represented by the Murray-Davies equation (3) of a monochrome (monochromatic) halftone dot printed matter The rate “R” can be expressed as a general equation as follows. R = Rp (1-a + aRs) (5) In the above formula (5), each symbol means the following. Rp: light reflectance of the underlying paper. Rs: the light reflectance of the solid portion of the printing ink when the light reflectance of the underlying paper is set to 1. a: Halftone dot area ratio per unit area. R: Light reflectance (theoretical value) of monochrome halftone dot printed matter.

According to the present invention, the ODG described in the above formula (5) is used.
It incorporates a correction term that rationally and quantitatively corrects (corrects) the effect. As described above, the correction term for correcting the ODG effect of the present invention is largely characterized in that a correction function (quadratic equation) shown below is employed. f (a) = ka (1-a) (6) A correction function f (a) = ka (1-) for correcting the ODG effect used in the present invention. a) is a quadratic equation, and when a = 0 or a = 1, f (a) = 0, a = 0.
In the case of 5, f (a) = maximum. In the correction function f (a) = ka (1-a), the correction coefficient (k) is Murray-Davies when a = 0.5.
That the theoretical value calculated by the formula (3) can be approximated to the light reflectance (R) of the actually measured value, that is, the value of the height of the quadratic equation as the correction function is adjusted by the correction coefficient (k). Have the property of being able to

From the above, the theoretical equation for theoretically calculating the light reflectance of a single-color print according to the present invention is a Murr correction term consisting of the quadratic equation for correcting the ODG effect.
By incorporating it into the ay-Davies equations (3) and (5), the following equation (7) is obtained. R = Rp {1-a + aRs-ka (1-a)} (7) Note that the theoretical formula for predicting the color density of the monochromatic print of the present invention, that is, the formula (7) is , R, G, and B filters, the optical reflectance “R” is measured. As will be described in detail later, the spectral reflectance “Rλ” is also satisfied.

As described above, Mu is defined as a theoretical expression for predicting the color density of an actual printed matter, in particular, a theoretical expression incorporating correction of an ODG (optical dot gain) effect.
Equation (4) of Yule-Nielsen based on equation (3) of rray-Davies and equation (7) of the present invention are shown. Here, in order to more objectively see the position of the means for correcting the ODG effect of the present invention with respect to the prior art, ODG
Some other research and approaches to (optical dot gain) will be considered a bit.

(1) Ruckdeshel and Hauser wrote the Yule-Nie
lsen's coefficient (n) value is physically analyzed ("Appl.O
pt., 17,3376 (1978) "). They convoluted the point spread function for the light of the underlying paper and the transmission distribution of the dots,
The result is compared with the expression (4) of Yule-Nielsen, and the coefficient (n) value is determined so that the two agree. They are n
The value range is 1-2, (i). When n = 1, the surface of the underlying paper is in a mirror state, (ii). When n = 2,
It states that the surface of the underlying paper is in a perfect light diffusion state. Also, they state that (iii). When the dot area ratio (a) is smaller than 50%, the n value indicates one value, and (iv). The dot area ratio (a) is larger than 50%. In this case, the n value is not constant but depends on (a). Furthermore, they apply that theory to photography. However,
Their theory is not strictly applicable to prints printed with printing inks. The reason is that the amount of ink transferred from the printing plate to the printing medium (printing paper) fluctuates during printing, and the amount of ink transferred is not stable depending on each part of the printing surface.

(2) Nagayama, Yuasa and Sanpin report the results of examining the effect of ODG on the effect of the halftone dot shape of the laser printer by simplifying the method of Ruckdeshel and Hauser. Bulletin of the Japanese Society
of PrintingScience and Technology, 28,366 (199
1) "). They state that the correlation between ODG and dot perimeter is very strong, but the correlation with the point spread function is small.

(3). Inoue, Tsumura, Miyake,
It is described that the n value can be derived by a convolution of the point diffusion function obtained from the above, a predetermined halftone dot area ratio (50%), and the transmittance of an image having a constant solid light density (“Prep
rint of the 96th Spring Conference of Japanese Soci
ety of Printing Science and Technology, 53 (199
6) ").

(4) Arney and Katsbe note that, in the case of a halftone printed matter in a thermal transfer printer, the light reflectance of the halftone dot and the paper between the halftone dots varies depending on the halftone dot area ratio (a). The probability that the light incident from the paper is reflected by the paper and returns to the halftone dot portion, and the probability that the incident light from the paper portion between the halftone dots is reflected by the paper and exits the halftone dot portion, is both a halftone dot. It is a function of the dot area ratio (a), and these functions are determined by defining one common index in the equation. When their probabilities are determined, the halftone dot / paper reflectance and halftone dot area ratio (a) It is shown that by substituting these into the equation (3) of Murray-Davies, the light reflectance (hence, the color density) of the halftone dot print can be expressed (see "J. Imag. Sci.Techn
ology., 41, 633 (1997) ").

(5). GLRogers, when given a point spread function (PSF) of paper with respect to light, a halftone dot of a round dot, a halftone dot by a convolution of a dispersion pattern and a point spread function (PSF). The reflectance of the printed matter was expressed as a mathematical expression, a phenomenological photon (photon) diffusion differential equation in paper was established, and the above equation was solved by introducing the initial conditions of the paper surface to obtain a point diffusion function. In addition, the reflectance of halftone printed matter is also derived from the probability of the transfer condition of photons (photons) in paper ("J. Imag. Sci. Technol., 41, 643").
(1997) "). Although not directly shown in his paper, the following ODG correction term can be derived by modifying his equation. R = Rp [1-a + aRs- (1- ◆ Rs) ² · a (1-a1 ^-s )] (8)

A correction term for correcting the ODG effect in Rogers equation (8), that is, (1- （Rs) ² · a
(1-a ^1-s ) is the correction term k · a (1-a) of the present invention.
It corresponds to. In the Rogers equation (8), if s = 0, that is, if the paper is completely scattered, Roge
The correction coefficient (1- ◆ Rs) ² of rs is the correction index k of the present invention.
Is equivalent to As described above, Rogers theoretically led the ODG effect by regarding paper as being isotropic and homogeneous, and performed excellently with respect to the theoretical treatment of the ODG effect. However, when the theory is applied to the printing field, the relationship between the processing of each of the variables in the theoretical system is not clear when various variables in the printing practice are considered. On the contrary,
For the purpose of correcting the ODG effect, the introduction of the correction term of the present invention is extremely practical and practical. This will be described in detail later. A print sample was prepared, and the difference in light reflectance corresponding to the actual ODG was measured using the above-mentioned Yule-N.
It can be confirmed by measuring using the ielsen equation (4), the equation (7) of the present invention, and the Rogers equation (8), and comparing the three. Needless to say, the theoretical formula of the present invention is the simplest of these three theoretical formulas.

As described above, the present invention makes it possible to rationally and accurately correct the ODG (optical dot gain) effect in the state where the halftone dots are overprinted, even if there are various fluctuation factors in the printing practice. Is what you can do.

That is, the expression (7) of the present invention is a theoretical expression for predicting the color density of a color print, and
Equation (2), in particular, the light reflectance of paper is set to 1, and the same relational equation of light reflectance (R) and halftone dot area (a) as the equation (3) of Murray-Davies of a monochromatic image is obtained. A correction term [f (a) = ka · (1−1) that can rationally correct the ODG effect.
a)], each color plate (C /
The “print color” of the printed matter can be expressed using the dot area ratio (a) of the (M / Y / BK plate) as a variable.

The present invention provides the above-mentioned results, that is,
Before printing in advance, a printing plate (color plate) of C / M / Y / BK is produced, for example, with the result that the “print color” can be reasonably predicted using the dot area ratio (a) as a variable. By applying the sometimes necessary gradation conversion curve (color separation curve), it is possible to produce (predictably) a print of a desired "print color" before printing in advance. A method for producing a color dot print can be provided.

In particular, as will be described in detail later, in the method of producing a color halftone print, the present invention relates to a method of manufacturing a color halftone print from a color original image (continuous tone) which is a core elemental technology. As a gradation conversion method (gradation conversion method from continuous gradation to halftone gradation) when producing a gradation, the dot gain (DG) which has been difficult to be quantitatively treated in the industry described above is used. Problem, UC when using ink version (BK version)
Incorporating (weaving) means to comprehensively solve problems such as A (addition of undercolor) and UCR (removal of undercolor), in advance (in advance)
A new gradation conversion method that can guarantee a high degree of color consistency (more specifically, a halftone dot of each color (C, M, Y, BK version) that can guarantee a high degree of color consistency) It is intended to provide a method for setting the area ratio (c, m, y, bk).

According to the present invention, as described above, four colors (C, M,
Y, BK ink), a new gradation conversion method that guarantees a high degree of color matching in the production of color halftone prints, more specifically, a dot area ratio of each color plate that guarantees such a high degree of color matching (C, m, y, bk). In the technique for setting the dot area ratio (c, m, y, bk) of each color plate that guarantees a high degree of color matching, as described above, the dot gain (D
G) problems, especially optical dot gain (OD
The problem G) is a big problem.

Other important problems include a gradation proportional compression method for continuous gradation of a color original to a halftone gradation, a masking process for dealing with improper absorption of printing ink, and a black plate (BK plate).
As described above, there is a problem of quantification of UCA and UCA in use, and a problem of mechanical dot gain (MDG) on a printing press. However, all of these problems must be dealt with in consideration of the dot thickening phenomenon (DG effect) in printing practice.

The method of correcting the ODG effect according to the present invention will be described below. In particular, a method of incorporating the correction term of the ODG effect of the present invention into Pollak's equation (2), which is a theoretical equation for predicting the color density of a color print, will be described.
Method of using the correction amount of the DG effect for gradation conversion work for producing each color plate (C / M / Y / BK plate) (new OD
A method of setting a gradation conversion curve in which the G effect has been corrected will be described.

(1) ODG of the present invention to Pollak's formula (2)
Incorporation of effect correction term (method using R, G, B filter light reflectance): When the ODG (optical dot gain) effect is represented by light reflectance (R), the light reflectance of paper Rp = When it is assumed that 1, the term of each monochromatic image in Pollak's equation (2) is expressed by Murray-Davies' equation (5) regarding the monochromatic image,
It is the same as (1-a + aRs). Therefore, the light reflectance (R) of the ODG effect is the actual (1−a + aRs) value (theoretical value) and the actual monochrome (monochrome) halftone dot printed matter having a halftone dot area ratio of “a”, In addition, it is a difference from a light reflectance value (measured value) actually measured assuming that the light reflectance of the paper is 1. Generally, the value of the actually measured light reflectance is smaller than the theoretical value calculated from the Murray-Davies formula (5) (1-a + aRs).

D. Difference in light reflectance corresponding to the amount of correcting (correcting) the ODG effect; R (difference of reflectanc
e) can be formulated as follows: D. R = (1−a + aRs) − (measured light reflectance) (9) Then, a correction term for correcting the ODG effect of the present invention,
The correction amounts (DR) in the Yule-Nielsen correction term and the Rogers correction term are given by the following (10) and (1), respectively.
This is formulated by equations (1) and (12). (i). Correction term of the present invention: R = k · a (1-a) (10) (ii). Yule-Nielsen's correction term: R = (1−a + aRs) − (1−a + a10− ^{Dsc / n} ) ⁿ (11) (iii) Rogers correction term: R = (1- ◆ Rs) ² · a (1-a ^1-s ) (12)

<Reference Example 1> (Regarding the validity of the method of correcting the ODG effect of the present invention by a quadratic equation): Here, the above (10) to (10) relating to the monochrome printed matter
The validity of the method of correcting the ODG effect by the equation (12) will be discussed based on experimental data. It should be noted that if the conclusion is anticipated, the method of correcting the ODG effect based on the expression (10) according to the present invention can sufficiently withstand practical use.

The outline of the experiment is as follows. (1). Manufacture of halftone dot printed matter: (a). A color target (FUJICHROME PROVI
A) was used. (B) C / M / Y / BK net positive films were prepared using a total scanner system (Cytex). (C) The shape of the halftone dots was square dots, and the screen ruling was 175 (LPI). (D) Screen angle is C15 °, M45 °, Y90
° and BK75 °. (E) Printing was performed with a lithographic proofing machine. (F) The PS plate used was FPP-B manufactured by Fuji Film Co., Ltd. (G) The printing paper used was Tokishi Art, an art paper manufactured by Mitsubishi Paper Mills. The continuous weight of the paper (weight of 1000 sheets of 788 mm × 1091 mm) was 135 kg. (H) The printing ink is TK For4 CIL manufactured by Toyo Ink Manufacturing Co., Ltd.
It was used. (I) The printing order was BK, C, M, and Y.

(2) Measurement of Light Density and Halftone Area Ratio of Halftone Printed Sample: <a> The light density value (D) of halftone printed matter (sample) was determined by Macbeth RD.
914 Measured with a densitometer, this light density value (D) is calculated as R = 10 ^-D
Was converted to light reflectance (R) by the following relational expression (density formula). <B> The halftone dot area ratio of the sample was measured using a computer connected to a microscope, a CCD camera and a monitor (CRT), using image processing software MacSCOPE manufactured by Mitani Corporation. <C>. The halftone dot image of the sample is magnified 100 times with a microscope, and CC
It was taken into the PC from the D camera and displayed on the display. A frame in which a total of nine halftone dots, that is, three vertically and three horizontally, was set on the display, and image processing was performed only within this frame. This is to avoid a biased measurement when one dot is selected, since the dot shapes are not exactly the same. <D>. Convert the color image of each single-color halftone print in the frame into a gray image. Then, in the binarization process, the brightness histogram of the gray image forms two peaks at the halftone dot portion and the paper portion between them, and the brightness at the lowest part of the valley between the two peaks is set to the threshold value. (Shreshold value). <E>. The dot area ratio was determined by measuring the number of pixels of the binary image of the dot within the frame. In the case of the yellow (yellow) single-color halftone dot print, the contrast between the brightness of the halftone dot portion and the brightness of the paper portion is low, and it cannot be separated into two peaks. Therefore, the image is separated into B images by a color separation method. To perform a binarization process. In addition, the binarized halftone image is always monitored by visually comparing the original color halftone image on the monitor.

FIGS. 2 to 5 show C (FIG. 2), M (FIG. 3),
Y (FIG. 4) and BK (FIG. 5) halftone dot area ratios (measured values) of color target portions and solid portions of halftone prints of each color separation
, The reflectance of each of the R, G, and B filters assuming that the reflectance of the paper is 1, is determined. R (Differential R
eflectance, a difference in light reflectance, that is, an amount for correcting the ODG effect), and plotted against a dot area ratio (Dot area). In each figure, three kinds of actually measured values (Measured DR 1, 2, 3) indicate that the same patch (the same scale patch of the gray scale portion) was measured at three positions, that is, upper, middle, and lower. I have. In each figure, the parts of the patches with dot area ratios of 0.08, 0.59, 0.61 are:
Variations in the measured values at the three locations are seen, but less at other locations. Rather, the variation between patches seems to be greater. These variations are believed to be indicative of the instability of the ink transfer in the printing process.

In the graph of the actually measured values of the halftone dot printed matter in FIG. 2, a dashed line is a correction curve symmetrical to the left and right of the present invention, a two-dot chain line is a correction curve by Rogers, and a solid line is Yule-Nielsen. FIG. These curves were obtained by adjusting the parameters of each equation so as to have the same value near the halftone dot area ratio of 0.5.In contrast to the symmetric correction curve of the present invention, the Rogers correction curve is It can be seen that the correction curve of Yule-Nielsen is tilted to the right.

The measured values of the M halftone dot printed matter in FIG. 3 show that when the halftone dot area ratio is 0.65 or less, even the same patch has large variations depending on the measurement location and large variations between patches. Similar to the case of C, when the values of the three types of correction curves are aligned near the halftone dot area ratio of 0.50, the correction value is smaller than that of the case of C, and in this case, the Rogers correction curve has a feature that is strongly inclined to the left. , Also Yu
The le-Nielsen correction curve is characterized by a strong slope to the right.

In the measured values of the Y halftone dot printed matter in FIG. 4, the variation depending on the location within the same patch is seen over the entire halftone dot area ratio, but the change between the patches is almost mountain-shaped. When the values of the three types of correction curves are aligned near the halftone dot area ratio of 0.50 in the same manner as described above, the three become substantially the same correction curves.

FIG. 5 shows that the actually measured value of the BK halftone dot printed matter is R
(Red) is a light reflectance difference (DR) obtained from a light density value measured using a filter. The reason for using the R (red) filter is that in the case of a BK halftone print,
The optical density measurement values of any of the filters G and B have almost no difference and look the same in visual observation (Visual). However, as will be described in detail later, for example, Pollak's This is because, when introducing (incorporating) the correction term into the equation, it is extremely effective to use the light reflectance difference obtained from the R (red) filter light density measurement. In FIG. 5, there is considerable variation in measured values depending on locations within the same patch, but the distribution of measured values as a whole is substantially mountain-shaped. When the values of the three types of correction curves are aligned near the halftone dot area ratio of 0.50, it is considered that the Rogers correction curve inclined to the left most represents the distribution of measured values.
The Yule-Nielsen correction curve appears to be too far to the right of the measured value distribution.

Table 1 below shows correction coefficients (hereinafter also referred to as correction parameters) of correction formulas (theoretical formulas) serving as bases of the respective correction curves for correcting the ODG effect shown in FIGS. That is, the correction parameter (k) of the correction curve of the present invention, the parameter (1-s) of the Rogers correction curve, and Yu
13 shows le-Nielsen's correction parameter (1−） Rs) ² and (n). As for the value of the correction parameter, it can be seen that C and Y are almost the same value, and M and BK are almost the same value. Table 1 shows the values of (1- ◆ Rs) ² corresponding to (k) in the correction formula of the present invention in terms of Rogers' formula. In this case, as the value of (1-s) is closer to 1, (1-s)
◆ Rs) ² value is seen to have become close to the correction value of the parameter (k) of the present invention.

[0070]

[Table 1]

The above-mentioned theoretical formulas relating to the correction term of the ODG effect of a single-color image all assume that the light reflectance of the underlying paper (printing paper) is 1 (Rp = 1). In the halftone dot printed matter, one color (for example, C) is already imprinted on the printing paper and another color (for example, M or Y)
The theoretical formula cannot be directly applied to an actual four-color halftone dot printed matter.
In other words, each color (C, M, Y, B) in the Pollak (2) equation
K) to the term corresponding to the above correction term [theoretical equation (10)
To (12)] cannot be directly introduced. Therefore, a method of incorporating a correction term (theoretical expression (10)) for correcting (correcting) the ODG effect of the present invention into Pollak's expression (2) for a four-color halftone print will be described below. Needless to say, this method of incorporating the correction term is one of the major features of the present invention.

Hereinafter, the correction term [theoretical formula (10)] for correcting (correcting) the above-mentioned ODG effect of the present invention is expressed by Pollak
The method of incorporating into the equation (2) is (1) using the R, G, B filter light reflectance (light density) of each color, and (2) using the R, G, B spectral reflectance of each color. In the case of adoption, description will be made in order.

(1) ODG of the present invention to Pollak's formula (2)
Correction term for correcting (correcting) the effect [theoretical formula (1)
0)) (method using R, G, B filter light reflectance): As is well known, four colors (C / M / Y / BK)
Overprinted color halftone prints can be divided into a total of 17 color gamuts, including primary, secondary, tertiary, and white paper. Below, C (cyan, process blue)
The characteristics of the color gamut will be considered using a plate as an example. When seeing through a color halftone print using an R (red) filter having a complementary color relationship with the C plate ink, a portion where the C plate is printed, and a portion where the BK (sumi, black) plate is printed , Looks black. This fact will be described in detail later, but Poll
It is used when incorporating a correction term [theoretical expression (10)] for correcting the ODG effect of the present invention into the expression (2) of ak, and should be sufficiently noted.

The total halftone dot area ratio of the above-mentioned black portions (the portions on which the C and BK plates are printed) is calculated as follows:
The maltiplication theorem of el probability
probability) (see “J. Im
ag.Sci.Technol., 41, 653 (1997) "). The outline of the calculation method is as follows. That is, a portion where the C plate is not printed and where the BK plate is not printed corresponds to a blank portion in the halftone printed matter printed in these two colors. The overlapping area ratio of C and BK can be obtained by subtracting the area ratio of the blank portion from 1. When this relationship is generally expressed by an equation, the dot area ratios of the C and BK plates are c, bk
Then, (i). The area ratio of the portion where the C plate and the BK plate are not printed is (1-c) (1-bk), and (ii). The area ratio of the portion where the C and BK plates are printed (hereinafter, referred to as c ′) is
It is a value obtained by subtracting the above (1-c) (1-bk) from "1".

According to the present invention, when a correction term for correcting the ODG effect is incorporated into the term C of Pollak's equation (2), the halftone dot of BK is regarded as the halftone dot of C; When the ratio is c → c ′, that is, c ′ = [1-
(1-c) (1-bk)]. The concept of the present invention described above is that the correction of the ODG effect of the term C can be approximately corrected by the combined ODG effect of the C and BK versions.
(2) to correct the ODG effect of the C term. FIG. 6 illustrates the above concept.

In the present invention, when a correction term for correcting the ODG effect is introduced into the C term of Pollak's equation (2), (i). Is adopted as the dot area ratio (c ') which is considered to have increased. By definition, c ′ = 1− (1−c) (1−bk). (ii) The correction function f (a) = k of the quadratic equation of the present invention expressed by the above equation (6) with respect to the C term of the Pollak equation (2).
A (1-a) is incorporated. At this time, the above c 'is adopted as the value of a, and since the correction coefficient (k) is related to the C term, it is displayed as (kc), and the correction coefficient (k) is displayed. Function f (c ') =
kc · c ′ (1-c ′) will be incorporated.

As described above, Pollak's equation (2) incorporating the correction term for correcting the ODG effect of the term C of the present invention is expressed as follows. R = Rp {1-c + cRsc-kc.c '(1-c')} (1-m + mRsm) (1-y + yRsy) (1-bk + bkRsbk) (13) where c '= 1- (1-c) (1-bk). Equation (13) is a theoretical equation for correcting the ODG effect of the C term of the four-color halftone print image employed in the present invention.

Similarly, when the four-color color halftone print is viewed through using a G (green) filter that is complementary to the M-plate ink, the printed portions of the M-plate and the BK-plate appear black. In the present invention, the correction of the ODG effect of the M term is approximately corrected by the combined ODG effect of M and BK, similarly to the correction means of the C term using the above fact. As can be easily inferred from the theoretical formula (13) for correcting the ODG effect of the term C, the theoretical formula of the present invention for correcting the ODG effect of the term M is as follows:
It is shown by the formula. G = Gp (1−c + cGsc) ｛1−m + mGsm−km · m ′ (1−m ′)｝ (1−y + yGsy) (1−bk + bkGsbk) (14) where m ′ = 1- (1-m) (1-bk).

Similarly, when a four-color color halftone print is viewed through a B (blue) filter having a complementary color relationship with the Y-plate ink, the portions where the halftone dots of the Y-plate and the BK-plate are printed appear black. The present invention uses the above-described fact to correct the ODG effect of the Y term in the same manner as the correction means of the C term.
The correction is made approximately by the combined ODG effect of K. As can be easily inferred from the theoretical formula (13) for correcting the ODG effect of the C term, the theoretical formula of the present invention for correcting the ODG effect of the Y term is represented by the following (15).
It is shown by the equation. B = Bp (1-c + cBsc) (1-m + mBsm) {1-y + yBsy-kY.y '(1-y')} (1-bk + bkBsbk) (15) where y '= 1- (1-y) (1-bk).

Reference Example 2 (Relevance of Theoretical Equations (13) to (15) for Correcting the ODG Effect of the Present Invention) Next, the following Pollak equation (2) employed in the present invention is used. ODG
Theoretical formula (13) incorporating a correction term for correcting the effect
Consider the validity of (15). Since the theoretical formulas (13) to (15) of the present invention modify the formula (2) of pollak, the formulas (13) to (15) may be hereinafter referred to as a modified pollak formula (Modified Pollak Equation). In FIGS. 7 to 9 described later, the theoretical formulas (13) to (15) of the present invention are described as “Modified Pollak Eq.”.

Next, the theoretical values according to the theoretical formulas (13) to (15) for correcting the ODG effect of the present invention are obtained by calculating the dot area ratio (C / M / Y / BK plate) of each color plate (C / M / Y / BK plate). c, m,
y, bk) in order to verify how close the measured values (spectral reflectance of each color) of the color prints produced by variously combining the color original images can be to the color target (standard). 36 of the color area of the original)
The color was selected and proof printing was performed, and a comparison was made between the two (the color target and the proof printed after plate making). The comparison operation is performed for the selected color area (patch).
The R, G, and B filter light densities (D) were measured, converted to light reflectance (R), and the theoretical values and the measured values were compared.

The selected color area portion (patch) includes (1).
All hue (H) is 1 in lightness L ^* 1 and saturation C ^* 3 series
12 colors divided into two (AL), (2) lightness L ^* 2, saturation C
^* 12 colors (A to L) obtained by dividing all the hues (H) into 12 in the 3 series. (3). Lightness L ^* 3, saturation C ^* All hues (H) are divided into 12 in the 3 series (A to L). 12 colors, total 3
There were six colors. Since the description of the work contents of the comparative study becomes long, the work contents of the comparative study regarding the 12 colors (1) of the above-mentioned selected colors will be described below. Although the other colors are not described, the same result as that of the 12 colors (1) is obtained.

Table 2 below shows the measured values of the dot area ratios of the C / M / Y / BK color separations of the patches (3A) to (3L) of the 12 colors of (1).

[0084]

[Table 2]

FIGS. 7 to 9 show (1) the measured value (Ref) as the light reflectance (Reflectance) through the R, G, B filters.
(2) theoretical value (by Pollak Eq.) based on Pollak's equation (2), and (3) the above-mentioned method adopted by the present invention incorporating the correction amount of the ODG effect into Pollak's equation (2). Theoretical value by theoretical formulas (13) to (15) (by modified
Pollak Eq.).

From FIG. 7 to FIG. 9, the following is considered.
BK halftone dots are overprinted on the L ^* 1 series. Therefore, in the correction of the ODG effect, it is possible to verify the effect of the combined correction of the complementary color filter light of each color of the ink and the filter light of the BK except for the case where the color is solid. For the R light, all colors (12
Color) has been completely corrected. For the G light, satisfactory correction has been made for all colors.
With respect to the B light, no correction is applied since the Y and BK halftone dots are hardly overprinted with respect to the blue and purple colors of 3-I and 3-J. Further, the red-purples of 3-K and 3-L are excessively corrected.

Here, the results of other color areas (patches) will be described briefly. The correcting means of the present invention was 100% satisfactory for the 12 colors of L ^* 2 and chroma C series. In addition, L ^* 3, 1 of chroma C series
Even for the two colors, a considerable correction effect was obtained, and the uncorrected portion was an area where the halftone dot area ratio of each of the C, M, and Y colors was extremely small or 0 (zero). .

As described above, the correction means for correcting the ODG effect of the present invention, more specifically, the theoretical equation (2) of the form in which Pollak's equation (2) in which the light reflectance of paper is separated as a correction equation is modified The correction means employing (13) to (15) are extremely useful because their theoretical values are very similar to the measured values of the R, G, B filter light reflectance. In addition,
The theoretical value (calculated value) can be made closer to the actual value by introducing the ODG effect and the correction of reciprocity law failure of solid printing by the product of the terms of paper, C, M, Y, and BK. What you can do is color reproduction of printed matter by overprinting halftone dots of each color (color reproduction,
This indicates that the principle of color reproduction is subtractive color mixing.

The theoretical expressions (13) to (15) in which the correction term for rationally correcting the ODG effect of the present invention is incorporated into Pollak's expression (2) are, as described above, (i). Single color (C
/ M / Y / BK), the correction of the ODG effect for a single-color halftone dot print is made by adding a quadratic equation [f (a) = ka (1) as a correction term to Pollak's equation (2). -A))
Knowledge that it is practically sufficient to incorporate
i). Correction of the ODG effect on a general color halftone print, that is, a four-color overlaid color halftone print, is performed by incorporating (introducing) the quadratic equation as the correction term into Pollak's equation (2). , R, C, M, Y, BK with respect to the dot area ratio of each color
From the comparison between the measured values of the G and B light reflectances and the theoretical values based on Murray-Davies's equation (3) (Note 1), it is found that the ODG effect occurs when complementary light (R, G , B)
For BK, R,
The finding that the G and B trichromatic lights are generated at almost the same level.
Finding that it is effective to use a light reflectance that combines the plate and BK plates, and ・ Demich, which expresses the degree of halftone dot overlap using the multiplication theorem of probability
Using the formula of el (this formula is also incorporated in the formula of Pollack (2)), for example, in the case of the C plate, all the printed portions of the C and BK plates are printed in the “C plate”. It is devised based on the finding that it is practically sufficient to correct the term C using the integrated dot area ratio (Note 2). (Note 1): Pollak's formula (2) is the light reflectance (R) when the light reflectance of paper in a four-color print is "1".
And the halftone dot area ratios (c, M, Y, BK versions)
m, y, bk). The term of each color plate, for example, the term C corresponds to the Murray-Davies equation (3) relating to the C-plate printed matter (monochromatic image). (Note 2): Quadratic equation as a correction term for correcting the ODG effect of the present invention, that is, f (a) = ka (1-a).
In the case of the C-plate, c ′ =
1- (1-c) (1-bk) is adopted.

(2). ODG of the present invention to Pollak's formula (2)
Correction term for correcting (correcting) the effect [theoretical formula (1)
0)] (method utilizing R, G, B spectral reflectance): Next, ODG (optical
As another correction method for correcting the dot / gain effect, “O1” of the present invention described in “(1).
A correction term for correcting (correcting) the DG effect [theoretical formula (1)
0)], a method using “spectral reflectance” instead of “incorporation method (method using R, G, B filter light reflectance)” will be described. As a correction means for correcting the ODG effect employed in the present invention, a correction term using a spectral reflectance is incorporated into Pollak's equation (2), whereby the R, R
The ODG effect can be rationally corrected rationally in exactly the same way as the method using the G, B filter light reflectance.

The Pollak equation (2) can be formulated using the spectral reflectance values as follows. Rλ = Pλ (1-c + cRscλ) (1-m + mRsmλ) (1-y + yRsmλ) (1-bk + bkRsbkλ) (16) In the above formula (16), each symbol means the following. . <1> .c, m, y, bk: C, M,
Halftone dot area ratio of Y, BK plate <2> .Rλ: Spectral reflectance of color halftone printed matter <3> .Pλ: Spectral reflectance of paper (printing paper) as a base <4> .Rscλ, Rsmλ, Rsyλ , Rsbkλ: The spectral reflectance of the solid area (solid area) when the spectral reflectance (Pλ) of the underlying paper (printing paper) of the C, M, Y, and BK color plates of the color halftone print is set to 1.

The correction function for correcting the ODG (optical dot gain) effect using the spectral reflectance can be easily understood from the correction function (6) relating to the R, G, B filter light reflectance. So that you can
The correction function when using the spectral reflectance can be formulated as follows. (i). kcλ · c (1-c) (ii). kMλ · m (1-m) (iii). kYλ · y (1-y) (iv). kBKλ · bk (1-bk) …… ............ (17)

The correction function (1) using the spectral reflectance
In equation (7), kcλ, kmλ, kYλ, and kBKλ are
It means “spectral correction coefficient” for the correction function of each color plate of C, M, Y, and BK. In the correction function (6) employing the R, G, and B filter light reflectances, it is simply referred to as a "correction coefficient".

Correction Function Using the Spectral Reflectance (17)
The precondition for incorporating the equation into the Pollak equation (16) of the spectral reflectance format is that the equations (6) and (13) to (15) using the R, G, and B filter light reflectances are used. The contents are exactly the same as those described above. This is referred to as the spectral reflectance (R
Briefly reconsidering the case of employing λ), it is as follows. (1) The wavelength region in which the ODG effect needs to be corrected is C,
In the case of each of the M and Y colors, it is the light absorption wavelength range of each color, and for BK, it is the entire visible wavelength range. (2). When the halftone dots of each color plate (C, M, Y version) and the halftone dot of the black plate (BK version) overlap, for example, when the halftone dot of the C plate and the halftone dot of the BK plate overlap, Is expressed as [1- (1-c) (1-bk)] by the multiplication theorem of probability.
The ODG effect is corrected (corrected) by regarding halftone dots of the BK version as halftone dots of the C version. Note that the halftone dots of the M and Y plates and the BK
It is exactly the same when the halftone dots are overlapped.

The correction function (17) in the spectral reflectance format is incorporated (introduced) into the Pollak formula (16) in the spectral reflectance format using the preconditions (1) and (2).
Accordingly, the theoretical formula for correcting the ODG effect of the present invention can be formulated as follows. Rλ = Pλ ｛1-c + cRscλ-kcλ · c ′ (1-c ′)｝ ｛1-m + mRsmλ-kmM · m ′ (1-m ′) ｍ · {1-y + yRsyλ-kyλ · y (1-y ′) ) {1-bk + bkRsbkλ} ............ (18)

In the above formula (18), each symbol means the following. <1> .c '= 1- (1-c) (1-bk) <2>.m' = 1- (1-m) (1-bk) <3> .y '= 1- (1- y) (1-bk)

<Reference Example 3> (Regarding the validity of the theoretical formula (18) for correcting the ODG effect of the present invention): Next, the Pollak formula (16) of the above-mentioned spectral reflectance format adopted by the present invention. The validity of the theoretical formula (18) incorporating a correction term for correcting the ODG effect in the following will be considered.

That is, a color dot print sample was actually prepared, and the theoretical value of the theoretical formula (18) of the present invention relating to the correction of the ODG effect using the spectral reflectance was compared with the actually measured value. The validity of equation (18) is evaluated.

(I) Preparation of color halftone print sample: A color halftone print sample is prepared by using a color target (FUJI
Using CHROME PROVIA), net positive films for C, M, Y, and BK were created with a total scanner. In addition, the specific method of preparing the net positive film sample is as described in <Reference Example 1>.

(Ii) Measurement of spectral reflectance and halftone dot area ratio of color halftone print sample: <a>. Spectral reflectance (Rλ) of color halftone print sample was measured with C2000 color analyzer manufactured by Hitachi, Ltd. did. Measurement is performed by selecting 12 colors (12 colors obtained by dividing all the hues into 12 colors in 3 series of lightness L ^* 1 and saturation C ^* ) in the color area of the original (color target), where BK is overprinted. These patches of the print were measured by spectroscopy using a color analyzer, and the theoretical value of theoretical formula (18) of the present invention and the measured value were compared. <B> In addition, the measurement of the halftone dot area ratio of the color halftone dot printed matter sample and the binarization process of the halftone dot are the same as those described in <Reference Example 1>.

(Iii) Calculation of a correction coefficient (kλ) of a correction function (quadratic equation) for correcting the ODG effect: (a). A color halftone print sample prepared using a color target (FUJICHROME PROVIA) as an original In the above, the dot area ratio of each step of the color-separated printed matter in the gray scale portion was measured by an image processing device Mac SCOPE. (B) Using a color analyzer (C2000), each step of the gray scale is performed in a range of 380 nm to 780 nm.
The spectral reflectance at 41 wavelength points was measured every nm. (C) At each wavelength point, the horizontal axis indicates the dot area ratio, and the vertical axis indicates the spectral reflectance (Reflectance).
a) ODG effect (Murray-Davi in spectral reflectance format)
The theoretical value and the measured value obtained from equation (3) of es are plotted, and they are quadratic equation, f (a) = kλ · a (1-
a) (a indicates the dot area ratio), and the spectral correction coefficient (kλ) was determined by spreadsheet software (Excel). In addition,
41 spectral correction coefficients (kλ) were calculated for one color, and thus a total of 164 were calculated for the four colors C, M, Y, and BK.

FIG. 10 shows, as one example, the approximate curves of the ODG effect (measured value) and the correction function (quadratic equation) at the wavelength of 450 nm of C among the 164 spectral correction coefficients (kλ). It is shown. In creating the approximate curve, the spectral correction coefficient (kλ) of the correction function (quadratic equation) must be appropriately set, and this is shown in FIG. FIG.
Indicates a spectral correction coefficient (kλ) for each wavelength point of each color of C, M, Y, and BK.

Here, a correction function (quadratic equation) in the form of a spectral reflectance for correcting the ODG effect of the present invention described above.
Of the present invention and other ODGs
The correction coefficient in the correction method for correcting the effect is compared with the correction coefficient. Using R, G, B filter light reflectance (light density),
As a correction method for correcting the ODG effect based on the Pollak equation (2), there are Rogers equations (8) and (12) as described above. Rogers proposes equations (8) and (12) as light density equations that use the photon diffusion differential equation and that correct the ODG effect on monochrome (monochromatic) halftone dot prints. The term is (1- ◆ Rs) ² · a (1-a ¹ -s), which is the same as kλ · a (1-a) of the present invention. Where
In order for the Rogers correction coefficient to match the spectral correction coefficient of the present invention, s = 0 should be set. In this case, Rogers
States that there is no diffusion of photons into the paper.

The value of the spectral correction coefficient (kλ) of the present invention and the value
Correction coefficient in Rogers spectral reflectance format (1- ◆ Rs) ²
Were compared. FIG. 12 shows the values of the spectral correction coefficients (kcλ) for the C plates at each wavelength point (41). The Rogers correction coefficient is assumed to be (1-Rs). For example, the value of (1-Rscλ) is shown for the C-plate.

As shown in FIG. 12, in the light absorption wavelength range for the C-plate, the difference between the two is extremely small (0.
About 2). The results described above were the same for the other color plates. That is, the spectral correction coefficient (kMλ) for the M plate, the spectral correction coefficient (kYλ) for the Y plate, and BK
The spectral correction coefficients (kBKλ) for the plates were very close in both cases.

This indicates that the spectral correction coefficient (kλ) may be approximated using the spectral reflectance of the solid portion of each color. In this case, the spectral correction coefficient (kλ) of the correction function for each color plate is represented by the following equation (19). kcλ = 1−Rscλ kmMλ = 1−Rsmλ kYλ = 1−Rsyλ kBKλ = 1−Rsbkλ (19)

(Iv) Consideration of experimental results: The measurement results of the halftone dot area ratio of the color separation of each patch (3A to 3L of the color target) are the same as in Table 2 above.

FIG. 13 shows (1) actual measured values of spectral reflectance (Refl.) Of patches of a print sample of 3A among 12 colors of patches of the color targets (color originals) 3A to 3L.
(2) theoretical value of Pollak formula (16) in the form of spectral reflectance (Reflectance calculated by Poll
ak Eq) and (3) the theoretical formula of the present invention, that is, the theoretical value (Reflectance calculat) of the modified Pollck's formula (18)
ed by Modified Pollack Eq.). In the operation of the theoretical expression (18) of the present invention, the spectral correction coefficient (k
λ) employed the values shown in FIG. As is clear from the figure, Pollak's (16)
It can be seen that the theoretical value of the theoretical expression (18) of the present invention is much closer to the measured value than the theoretical value of the expression. The same result was obtained with other color patches, that is, the color patches from 3A to every other 3K.

FIG. 14 shows L ^* a ^* to make it easy to see the difference (difference) between the theoretical value of the theoretical formula for correcting the ODG effect and the measured value in the print sample of the 12-color patches of 3A to 3L ^. b ^* color difference of colorimeter △ E
It is represented using. That is, FIG. 14 shows (a) the color difference between the theoretical value and the actually measured value of the Pollack equation (16) (pollak Eq.) (B) The theoretical equation of the present invention, that is, the modified Pollack (1)
8) The color difference between the theoretical value and the measured value when the spectral correction coefficient kλ = 1−Rs (Modified pollak Eq, k = 1−Rs), and (c) another theoretical formula of the present invention, That is, it was modified
Pollak equation (18) and spectral correction coefficient kλ = k
(Value shown in FIG. 11) (Modified Pollak
Eq, k = k) shows the color difference between the theoretical value and the measured value. In the figure, the spectral correction coefficients (kλ) are all indicated as (k).

As apparent from FIG. 14, in the theoretical formula (18) of the present invention, the color difference (ΔE) of the one using (k) as the spectral correction coefficient (kλ) (kλ = k) is po
1/3 to 1/2 of the color difference (△ E) of the value of equation (16) of llak
It can be seen that it is within ΔE = 5-10. In other words, it can be seen that the means for correcting the ODG effect according to the theoretical formula (18) of the present invention is extremely practical. Further, in the theoretical formula (18) of the present invention, C, M, and Y are used as the values of the spectral correction coefficient (kλ).
Utilizing the spectral reflectance (Rs) of each solid printed matter of (1)
9) Color difference (△ E) using equation (kλ = 1−Rs)
Is apt to be up to about 3 at the maximum in comparison with the above-mentioned one using the theoretical formula (18) of the present invention. Therefore,
This correction method is also practically useful.

The ODG effect correcting means for correcting (correcting) the ODG effect and predicting the color matching according to the present invention includes Demishel's assumption (probability multiplication theorem) regarding the overlapping state of the halftone dots, Assuming the density additivity of the solid portion (solid portion) and the like, as described above, the arbitrary halftone dot area ratios (c, c, m, y,
(2) of Pollak in a light reflectance type or a spectral reflectance type for expressing a printing color by a combination of (m, y, bk)
This adopts a theoretical equation in which a specific correction term for correcting the ODG effect is introduced into the equation or the equation (16). I have.

As described above, the correction method for correcting the ODG effect according to the present invention is as follows. (2) by introducing a specific correction term into Pollack's equation (16) using the R, G, B spectral reflectances, that is, based on a predetermined theoretical equation It is reasonable to do with In addition, the O of the present invention
The correction method for correcting the DG effect can reasonably cope with a change in the type of paper because a term representing the reflectance of the paper as a base is introduced in the theoretical formula as a base. This is a practically preferable correction method from this point of view.

As described above, the correction method for correcting (correcting) the ODG effect of the present invention is based on each color plate (C, M, Y, BK).
By combining the halftone dot area ratios (c, m, y, bk) of the printing plate, the printing color that can be reproduced can be accurately predicted in advance. This means that each color of a color chart collection for color management used in plate making, printing, and the like can be represented by a theoretical expression (formula).

As is well known, a plate making / printing engineer searches a color chart collection to find out what color should be reproduced at a predetermined portion (predetermined pixel) in a color film original, and finds each color capable of reproducing the color. Halftone dot area ratio (c, m,
y, bk) (for example, as shown in FIG. 13, c47%, m100%,
The user knows y85%, bk24%, etc., and sets a halftone curve (called a gradation conversion curve, a gradation conversion work curve, a color separation curve, a tone curve, etc.). However, the setting of the halftone photographing curve (gradation conversion curve) is not limited to the combination of the halftone dot area ratios of the respective color plates of the corresponding portion (predetermined pixel), but also to the color reproduction and tone reproduction of the entire color halftone print. From the viewpoint of both tone reproduction and gradation reproduction), it should be rationally set for the pixels in the entire region from the H section to the S section. DG (ODG and MD)
G) It is necessary to take into account correction of effects, theoretical setting of UCR and UCA, and the like. In consideration of these points, it is not an exaggeration to say that the setting of the halftone photographing curve (gradation conversion curve) is currently performed empirically by the setter.

Hereinafter, the respective color plates (C, C, C) for reproducing the color (color) and the color tone of the color original image on the color print image using the halftone dots while utilizing the above-described ODG effect correction method.
(M, Y, BK versions) A rational method for determining the dot area ratio (c, m, y, bk) to be set for each pixel in the H section to the S section, in other words, the correction of the ODG effect A method of setting a gradation conversion curve for producing a color halftone print in which a method is incorporated and color reproducibility is guaranteed will be described.

A method (R, G, B filter light) for incorporating the correction term (theoretical equation (10)) for correcting (correcting) the ODG effect of the present invention into the above-mentioned “(1). Pollak equation (2)”. And (2). A method of incorporating the correction term (correction term [theoretical equation (10)] for correcting the ODG effect of the present invention into the equation (2) of Pollak (R). , G, B spectral reflectance)), in order to rationally predict the color of the color halftone print image, MDG (mechanical dot gain) or ODG (optical dot gain).
(Dot gain), in particular, the ODG effect correcting means for correcting the ODG (optical dot gain) effect and achieving color matching has been described. that time,
In the above “(1) to (2)”, various theoretical formulas applied to the color prediction of the color halftone print, for example, the formula (1) of Neugebauer and the formula (1) of Neugebauer are used to improve the structure of the printed matter. The limitations such as Pollak's equation (2), in which the paper and ink to be expressed are separated, and Murray-Davies's equation (3), which deals with the relationship between the light reflectance of a monochrome image and the dot area ratio, were explained. In view of the limitations of these conventional methods, the present inventors have proposed (1).
Incorporation of correction term into equation (method using R, G, B filter light reflectance), (2). Incorporation of correction term into Pollak equation (2) (R, G, B spectral reflectance Method),
And a theoretical formula that can predict the color match by reasonably correcting the ODG effect.

A major problem left in the present invention is to establish a system for rationally producing four-color halftone prints based on these results. In particular, it is an object of the present invention to establish a rational setting method of a gradation conversion curve (tone curve), which is a core elemental technology in producing a four-color halftone print using these results. Hereinafter, this point will be described in detail.

As described above, ODG is added to Pollak equation (2).
Theoretical formulas for correcting the ODG effect of the present invention (the above (13), (14), (15), and (1)) in which a correction term (correction function) using a quadratic equation for correcting the effect is formed.
By using the expression 8), for example, a specific color (color of a specified specific color patch) of a book-format color chart collection used as a color sample at a plate making site can be reproduced. This is because the specific color on the predetermined patch of the color chart collection is a color plate (C, M,
Since the halftone dot area ratio (c, m, y, bk) of the Y, BK version is given (because it is given), the reproduction of the specific color by printing is based on the ODG effect described above. By using the theoretical formula for correcting
This is because the halftone dot area ratio in which the DG effect has been corrected can be obtained.

However, general color originals (for example, color film originals generally used as originals)
Is to be reproduced by printing, the situation is completely different. When reproducing color originals by printing (color reproduction), as is well known,
In a color original, each pixel in the entire area from the H section to the S section has various color (color) information, and a color halftone print image excellent in color reproducibility is produced from such a color original. In order to achieve this, how to perform the gradation conversion of each pixel in the H section to the S section, in other words, the halftone dot area ratio of each color plane (C, M, Y, BK plane) is assigned to each pixel. How to set, gray balance processing, masking processing, UCA and UCR processing with black plate (BK plate),
And a correction method for correcting the ODG effect described above and M
A method for rationally integrating (combining) correction methods for correcting the DO effect and the like must be considered.

In the case of producing a color halftone dot printed image, a part H to
Importance and complexity of gradation conversion of each pixel of each color plate (C, M, Y, BK plate) so as to guarantee a high degree of color consistency (color consistency) in the entire dynamic range of the S section Is incomparable with the simple color reproduction of a single color of a specific patch of the color chart collection described above. This can be easily understood by considering that in the production of a color halftone dot printed image, it is necessary to simultaneously satisfy the color reproduction of an extremely large number of pixels.

The present inventors have previously described image information (image information correlated with density) of a continuous tone color original as a dot area ratio (same as dot area% value, fractional dot areas). As a new tone conversion method for producing a color halftone print image which is excellent in tone reproducibility, that is, both tone (color tone) and density tone (gradation), for example, , Patent No. 1,
No. 886,821 and Japanese Patent No. 2,939,270. In the above-mentioned new gradation conversion method proposed by the present inventors, the former patent 1,886,82
No. 1 (Japanese Patent Application No. 63-114599, Japanese Patent Application No. 6-146)
No. 83) is based on a density information value (D) taken from a predetermined pixel of a color original (color film original) and a halftone dot area ratio (for example, C plate) based on a specific tone conversion equation. To a halftone dot area% value c). Also, the latter Patent No. 2,939,270 (Japanese Patent Application No. 1-135825,
Japanese Patent Application Laid-Open No. 3-3477) discloses a method for removing the characteristic (distortion) of a photosensitive film (original recording medium) of a color film original by using a photographic density characteristic curve of the photosensitive film to obtain density information of a predetermined pixel. A method of calculating a light amount value (a concept including an exposure amount) (X) from the value (D), and converting the light amount value (X) to a tone area ratio by a specific tone conversion equation. Things.

A tone conversion formula used for converting the continuous tone of a color original into the tone of a color print image, which is the core of the new tone conversion method proposed earlier by the present inventor. (Tonal conversion equation) is to convert the gradation of all pixels in the H to S parts of a color original so that a color halftone print image having excellent tone reproducibility is produced. . For this reason, the inventor
In the operation of this gradation conversion formula, it was difficult to quantitatively deal with the above-mentioned industry in the inking process and DG (dot / dot).
Dot (combination) means for quantitatively handling gain (effect) correction processing (ODG and MDG effect correction processing), etc., to create tone curves (halftone curve, gradation conversion curve) that are more suitable for platemaking practice Then, it was thought that a color halftone dot printed image that highly assures color consistency (color consistency) as planned in advance when designing the plate making may be produced by the tone curve.

According to the present invention, the DG having a great influence on the inking process and the color (color) reproducibility regarding the use of the black plate (BK plate) in the gradation proportional compression process based on the above-described idea. (ODG, MDG) Integrating elemental technologies in plate making, such as effect correction processing, gray balance processing, masking processing, etc., so that color matching (color consistency) can be performed in advance (before plate making).
To provide a new gradation conversion method that can highly guarantee the gradation.

The present invention is based on the use of a predetermined black plate (BK plate), that is, the dot area ratio (b) of a given BK plate (black plate).
In relation to k), the halftone dot area ratios (c, m, y) of the other color plates (C, M, Y plates) are quantified so that a high degree of color matching can be obtained. In addition, the present invention relates to a predetermined black plate (B
GCR (Gray Component Repla)
cement, removal of gray component) (CMY
It compensates for the shortage of CMY components due to improper absorption of ink by UCA (addition of undercolor), and quantifies the altitude so that the coincidence can be obtained. In the art, a UC that combines equal amounts of C, M, and Y ink components as a black plate (BK plate) is used.
R (Under Color Removal) is known. In the present invention, the GCR replaces the equivalent absorption of R, G, and B colors with a black plate (BK plate).
Strictly speaking, it is different from the UCR but may be understood as being homogeneous. As you can see from the above,
The gradation conversion method of the present invention uses GCR,
It is intended to rationally quantify UCR (under color removal) and UCA (under color addition) inking processing and DG (ODG, MDG) effect correction processing. Note that the above-described inking process and ODG effect correction process still largely depend on the experience and intuition of a plate making designer in the art.

A new gradation which can guarantee a high degree of color consistency (color consistency) by incorporating the rational inking process and the rational ODG effect correction process of the present invention will be described below. The conversion method will be described in detail.

The new gradation conversion method incorporating the rational inking process and the rational ODG effect correction process of the present invention provides a four-color halftone print which guarantees a high degree of color matching. In order to be able to manufacture, the dot area ratio (c, m, y, b) of each color plate (C, M, Y, BK plate) at a predetermined pixel point
k) is determined rationally. As will be described in detail below, in the present invention, the dot area ratio (c, M, Y, BK plate) of each color plate (C, M, Y, BK plate) for producing the above-described four-color color dot print which guarantees high color matching. , M, y, b
k) (however, in the present invention, bk is set as a given value) is finally obtained through various steps as described below. Therefore, the value of the dot area ratio determined in each of these steps is (c1, m1, y1),
It should be understood that (c2, m2, y2), (c3, m3, y3), etc., are ultimately determined as (c, m, y). In addition, with such understanding, the following description is easily understood. Furthermore, various theoretical formulas are described below, which are deeply related to the gradation conversion method of the present invention. To emphasize this, each equation will be described with a number of (100) or more. For example, the theoretical formula for the tone conversion method of the present invention is:
(100a), (100), (100-1), (10
Descriptions are given with numbers such as 1) and (110).

In the present invention, a tone conversion formula used for converting a continuous tone into a halftone when producing a halftone color halftone print image from a continuous tone color original. Are the patent specifications previously proposed by the present inventors (Patent Nos. 1,886,821 and 2,939,27).
No. 0), as shown below. yn = AH + [α (1-10− ^{γ · xn} ) / (α−β)] · (As−AH) (100a)

In the tone conversion equation (100a), each symbol means the following. xn: A value when the image information value at an arbitrary pixel point (n point) of the color document is normalized to a range of 0 to 1.0. (Note) The image information value at an arbitrary pixel point (n point) of the color original is, for example, 0.50 (H portion) to 3.00 as a density value.
(S section) and the like, but show values when the dynamic range of the H section to the S section is adjusted to 0 to 1. In addition,
The xn value need not be a specially normalized value as described later. yn: A dot area ratio (% value) set to a pixel point on a color halftone print image corresponding to an arbitrary pixel point (n point) of a color document. AH: halftone dot area ratio (% value) preset at point H on the color halftone print image corresponding to the brightest portion (point H) of the color document
Is shown. As: Halftone dot area ratio (% value) preset at S point on the color halftone print image corresponding to the darkest part (S point) of the color document
Is shown. α: surface reflectance of printing paper as a medium for expressing a color print image. (Note) In the present invention, hereafter, the α value may be treated as α = 1.0. In this case, it means that the surface reflectance of the paper is adjusted to 1. β: indicates a value defined by β = 10 ^−γ . γ: Indicates an arbitrary coefficient including the (Ds / n) value. However,
Ds is the solid density value of the color plate (for example, C plate), and n is Yule-Nie
Indicates the coefficient defined by lsen's equation (4).

In the tone conversion method of the present invention, which is based on the operation of the tone conversion formula (100a), the color original may be a color film original (transmissive original) or another type. Further, as the xn value, H part to
A value that does not normalize the dynamic range of the S section to 0 to 1 may be used. In this case, in order to ensure that the AH and As values scheduled at the H point and the S point can be reliably obtained, the xn value is obtained by subtracting the image information value xH of the H section from xn, that is, xn → (xn It is preferable to use -xH) and to use γ → γ / (xs−xH) as the γ value. Note that xs indicates the image information value of the S section. The above point can be easily understood by operating the gradation conversion formula (100a).

Further, when the color original is a color film original, the characteristic curve of the color film is used to remove distortion of image information due to the characteristics of a photographic photosensitive material (photosensitive film) of the color film. A value obtained by removing the distortion using a (photographic density characteristic curve) may be used. Removal of image information distortion by the photographic photosensitive material,
Characteristic curve (photographic density characteristic curve) that has been formulated (functionalized)
Can be easily obtained from For example, a photographic density characteristic curve is represented by D = f (x) in an orthogonal coordinate system of a D axis (vertical axis) indicating photographic density (D) and an X axis (horizontal axis) indicating exposure amount.
, The detected density value (D)
Thus, the image information value (x) which is not affected by the characteristics of the photographic photosensitive material can be easily obtained by using the function of D = f (x).

As described above, the gradation conversion formula (100a) used in the present invention uses the image information value (xn) as an independent variable,
(Yn) is a function expression with a dependent variable. The present invention uses a formula (100) proposed earlier by the present inventors as a tone conversion formula.
Although a) is used, the technical configuration of the present invention is completely new. In other words, the fact that the present invention utilizes the formula (100a) proposed by the present inventors does not deny any novelty or inventive step of the present invention.

The present invention is intended to produce a color halftone print image by multicolor (C, M, Y, BK) plate making.
First, as the first stage of the operation, the R, G, B system image information (xc, xM, xY) of a continuous tone color original is proportionally compressed (gradation conversion) into halftone gradations. Tone conversion formula (1
00a), C, M, and Y halftone dot areas for color reproduction in C, M, and Y systems from R, G, and B system image information (xc, xM, xY) of a color original image Ratio (c1, m1, y
Find 1). Note that the relationship between (c1, m1, y1) and (xc, xM, xY) in the first stage obtained as described above is, for example, a C version (C −plate) (tone conversion curve).

The tone conversion method of the present invention, more specifically, the dot area ratio (c, m, m) of each final color plate (C, M, Y plate)
The first step for setting y) is the gradation conversion equation (1).
00a), as xn → xc, xM, xY, the dot area ratio (c1, m1, y1) for each color plate (C, M, Y)
Is set. The proportional compression (gradation conversion) of the gradation in the first stage is performed by the following equations (100), (101), and (10).
2). The following equation (10
0) to (102), for example, the expression (1)
00), the γ value in equation (100a) is Yule-Neils
A value of γ = Dsc / nc using the n value of the equation (4) of en may be adopted. The n value in the above-mentioned Yule-Nielsen equation (4) is an optical dot gain (O
DG) can be regarded as a correction coefficient as described above. Accordingly, the first halftone dot area ratio (c1, m1, y1) obtained by the operation of the following equations (100) to (102) is:
It can be considered that the ODG effect is corrected by the above property of the γ value.

[0134] c1 = AHc + ^{[(1-10 -γ · xc) / (} 1-10 -γ) ] · (Asc-AHc) .................. ( 100) m1 = AHM + [(1-10 ^- ( ^{γ · xM} ) / (1-10− ^γ )] · (AsM−AHM) (101) y1 = AHY + [(1-10− ^{γ · xY} ) / (1-10− ^γ ) ] (AsY-AHY) (102)

The symbols in the above formulas (100) to (102) mean the following. The expression (1
00), and the other color plates (M, Y) have similarities, and thus description is omitted. 1) c1: Halftone dot area ratio at an arbitrary pixel point of the C plane image. 2) xc: Image information obtained through an R filter of a color original. Note that xM and xY are a G filter and a B filter, respectively.
5 shows image information obtained through a filter. 3) AHc: The halftone dot area ratio set in the H portion (lightest portion) of the C-plate image. 4) Asc: The dot area ratio set in the S portion (darkest portion) of the C-plate image. 5) γ: any coefficient including Dsc / nc. However, Ds
c is a solid density value of the C-plate image, and nc is a Yule-Nielsen coefficient, and these are R filter light reflectance (R
c) and the relational expression (Yule-Nielsen equation) R of the dot area ratio (c)
c = (1−c + c · 10− ^{Dsc / nc} ) ^nc is established.

The gradation conversion formula (100
a) and the characteristics of (100) to (102)
The details are described in the above-mentioned patent specifications (Japanese Patent No. 1,886,821 and Japanese Patent No. 2,939,270). The tone conversion formula can proportionally compress the tone (color tone and density tone) of a color original to a density range (dynamic range) in which the color original can be reproduced by printing, and color cast of a color original (color cast) It also has the characteristic that faded colors can be automatically corrected.

In producing a high quality color halftone dot printed image, each color plate (C, M, Y plate) is converted to a gray balance (gray b
It is important to set the balance so that the balance is maintained. The above-mentioned gray balance means that when the spectral reflectance of the paper by the R, G, B spectral filters is "1" in all the R, G, B filters, that is, when the printing ink (C, M, Y) is completely white. In the case where there is no illegal absorption of C, M, and Y inks, when the halftone dot area ratios (c, m, y) are the same (for example, c = y = m = 50%), in other words, gray (halftone) Means that the spectral reflectance of each color ink by the R, G, B spectral filters has the same ratio. If necessary, the above-mentioned condition for maintaining the gray balance is that when color plates (C, M, Y plates) having the same halftone dot area ratio (c = m = y) are overprinted, gray (neutral) Color) is a condition under which the color is developed.

Various methods can be considered for maintaining the gray balance, but the following method can be adopted in the present invention. That is, the above formulas (100) to
When (c1, m1, y1) is determined by employing (102), the variables (xc, xM, xY) of the respective expressions are determined by the following expressions (100-1) to (102-1). Use values. xc = xc '... (100-1) xM = (Dsc / DsM) .xM'... (101-1) xY = (Dsc / DsY) .xY ´ …………… (102-1)

In the above equations (100-1) to (102-1), (xc ′, xM ′, xY ′) represent R, G, B system image information (x
c, xM, xY). The method of maintaining the gray balance is based on the C plane (xc = xc
′), The R, G, B system image information (xc ′, xM ′, xY ′) received from the color original is calculated by the equations (100-1) and (10-1).
1-1) and (102-1) to process (xc, xM, x
Y), which is used in equations (100) to (102). In addition, the formulas (100-1) to (102-
1) is the same density (Dc = DM =) when the halftone dot area ratio is the same in each color plate (C, M, Y plate).
DY). In the present invention, the gray balance processing is performed according to the above-described equations (100-1) to (102-).
Equations (100) to (10) are used instead of the method using 1).
In the operation of 2), the value may be adopted by adopting a value that maintains the gray balance as the “γ” value of these equations.

In the present invention, the gradation conversion formula (10
0) to (102), each color plate (C,
The dot area ratio (c1, m1, y1) of the (M, Y version) is used as data for inking processing, that is, data for defining a given black version (BK version). In the present invention, the inking process is based on the idea of (1) replacing pixels in which R, G, and B colors are equally absorbed with a black plate (BK plate), that is, a GCR (Gray Component).
Based on the concept of “Replacement” (removal of the gray component), (2) the amount of replacement with black plate is determined by a predetermined black plate function (black plate curve).

In the present invention, each color ink (C, C) after being replaced with a black plate (BK plate) in relation to GCR.
M, Y), of course, the CMY component becomes insufficient due to the improper absorption component of each color ink, but this is corrected by the masking process described later. In other words, UCA (addition of a lower color) for compensating for the shortage of the CMY components is rationally processed by a masking process described later in the present invention.

In the present invention, as the black plate function (black plate curve) for defining the replacement amount to the black plate (BK plate), any function can be used as long as it is reasonably specified. it can. For example, as a given black plate (BK plate), a plate defined by a linear function (y = ax + b) can be used.

In the present invention, as described above, it is possible to use a function defined by a linear equation represented by the following equation (100b) as a given black board (BK board) function (black board tone curve). it can. bk = p (x−q) (100b)

The equation (100b) that defines the tone curve of the black plate (BK plate), and the characteristics and operating conditions of bk = p (x−q) are as follows. The x value is the amount of the gray (black) component of the R, G, B image information absorbed equally in each pixel, that is, the minimum (min) min (c1, m1, y
1) is shown. Also, p> 0, q is 0 (zero) or q>
0. Further, since the present invention is premised on the use of a given black plate (BK plate), the expression (100b) can be expressed as bk
It goes without saying that it is operated under the condition of> 0. The parameter q means that a black plate (BK plate) is inserted from the pixel point of x = q, and whether the black is added to the entire range (HS section) of the image (full black) depending on the value of q. Or whether to put black ink in a predetermined range (skeleton black). Below, ink version (BK
Another function formula that defines the tone curve of the version will be described.

It has been found that the black plate (BK plate) is rationally set based on the tone curve of the C plate set by using the above equation (100). −
No. 248768, US Pat. No. 5,134,494, U.S. Pat.
K2, 252, 469). For example, when the black plate (BK plate) is inserted from the halftone (M part) to the shadow part (S part), reflecting the plate making practice of the industry, the tone curve (black plate curve) is the same as the C plate curve. It can be determined rationally on the basis. At this time, the values of AHc, Asc, and γ, which are the parameters of the setting equation (100) for the C-plate curve, may be changed as desired.

As described above, the function for setting the tone curve of the black plate (BK plate) can be easily inferred from the equation (100) which is the function for setting the tone curve of the C plate. This is shown in equation (100c). bk = AHBK + [(1−10− ^{γ · xBK} ) / (1−10− ^γ )] · (AsBK−AHBK) (100c)

As described above, the setting of the tone curve of the black plate (BK plate) reflects the practice of plate making in the art. It may be set as follows. Therefore, to set the black plate curve using the above equation (100c),
As the operation conditions of the above equation (100c), a starting point (SP, Starting Point) and an ending point (EP, End) for inserting a black dot are used.
Point), for example, the starting point is a 20% (halftone dot) part of the C plane, the end point is a 95% part, the amount of black ink is (dot area ratio bk) 0 to 60%, and By setting a desired value (for example, γ / (xs−xH)) as the γ value of the expression (100c), the black plate curve can be rationally set by the expression (100c). The above (100
In the equation b), the xBK value is a normalized value (xsBK−xHBK)
= 1.0).

FIG. 15 shows an example of setting a tone curve of a black plate (BK plate). The comment for FIG. 15 is as follows. (A). The tone curve of the color plate (C, M, Y plate) in the figure is expressed by the above-mentioned gradation conversion formula (100), more specifically, (100) to (100).
This is set using equation (102). These color plates have not been corrected for the ODG effect yet. Setting condition of C-plate tone curve: Halftone dots of 3% in H portion and 95% in S portion were set to γ = 0.45.・ M and Y plane tone curve setting conditions: 3% for H section,
A 90% halftone dot was inserted in the S portion, and γ was set to 0.185. (Note) The γ value of the color plate (C, M, Y plate) is the dot area ratio of the M plate and the Y plate (m, y) at 50% of the dot area ratio of the C plate (c). Are set to be 40% respectively. This is to maintain the gray balance (color balance) when each color plate (C, M, Y plates) is overprinted. Needless to say, it is preferable to maintain the gray balance (color balance) by changing the γ value depending on the process ink (printing ink) used.

(B). The tone curve of the black plate (BK plate) in the figure is obtained by using the above-mentioned gradation conversion formula (100c) and
This is set based on the tone curve of the plate. The setting conditions of the BK plate tone curve: the dot area ratio of the C plate tone curve is 20% to 95%, and the dot area ratio of the black plate is 0 to 95%.
50% was added. Further, the γ value is -1.0
Two values, 0 and -1.5, were employed. (Note) The tone curves of the respective color plates (C, M, Y plates) shown in FIG. 15 are before the ODG effect correction processing according to the present invention.

In the present invention, in order to quantitatively process UCA or UCR, a given black plate (BK plate) is used.
Must be specified in a functional form as described above. In the present invention, the given black plate (B
K version) can be adopted as long as it is defined in a predetermined functional form such as a quadratic equation, in addition to the above.

In the present invention, the GCR
The amount of replacement with the black plate (BK plate) is specified in relation to the above. Then, in the present invention, C, M, and Y color component amounts (c1, m1, y1) before replacement with the black plate (BK plate)
Are the C, M, and Y color component amounts after replacement (c2, m2, y
2). The respective color component amounts (c2, m2, y2) after the replacement can be easily obtained by the following relational expression between the given bk amount and the respective color component amounts (c1, m2, y1) before the replacement. . For example, the following equation (10
3) is the inking process, that is, (c1) before the GCR process.
Means (c2) after the GCR process, which is equal to the sum of (bk) of the given black plate (BK plate) and the overlap between the two.

[0152]     c1 = c2 + bk−c2 · bk     c2 = (c1-bk) / (1-bk) (103)

[0153]     m1 = m2 + bk−m2 · bk     m2 = (m1-bk) / (1-bk) (104)

[0154]     y1 = y2 + bk−y2 · bk     y2 = (y1-bk) / (1-bk) (105)

When colors are reproduced in the C, M, and Y systems, masking for correcting improper light absorption of each color ink (including black ink) while taking into account the inking process and the ODG effect correction process. (Color correction) processing is essential. In the present invention, the Pollac equation (2) used as a base for correcting the ODG effect has a form in which correction processing (masking processing) of improper light absorption of each color ink can be performed. The masking (color correction) process of the present invention is performed under the inking process in a given BK version.
The halftone dot area ratio (c2, m2, y2) of each color plate (C, M, Y plate) obtained as described above is the overprint of the black plate and each color plate (C, M, Y, BK plate). Correction of light absorption irregularity of each color ink and correction of ODG effect at the same time, and halftone dot area ratio (c3, m3, y3, b
k) (where bk is given). The halftone dot area ratios (c3, m3, y3, bk) satisfying the above color matching conditions are expressed by the following formulas (106) to (106).
(108). The following equation (106)
In (108), for example, the expression (10)
The meaning of 6) is as follows. (1) On the left side and the right side, the correction function of the ODG effect represented by the above equation (7) is used to correct the ODG effect of the C plane. (2). The color information (specifically, c2) of the C ink after the inking process on the left side is changed to the color information (specifically, the color information when the four colors (C, M, Y, and BK) inks on the right side are overprinted. Typically, c3, m
(3, y3, bk) using the Pollak equation (2). The following equations (106) to (108)
It can be easily derived from the method of correcting the ODG effect of the present invention, Pollak's formula (2) relating to color prediction of color halftone dot printed matter, and the multiplicative theorem of probability.

[0156]   [1-c2 + c2.Rsc-kc.c2 (1-c2)]     = [1-c3 + c3.Rsc-kc. (C3 + bk-c3.bk)       (1-c3) (1-bk)] · (1-m3 + m3 · RsM)       · (1-y3 + y3 · RsY) · (1-bk + bk · RsBK)                                                   ............ (106)   [1-m2 + m2 · GsM-km · m2 (1-m2)]     = (1-c3 + c3.Gsc). [1-m3 + m3.GsM-kM.       (M3 + bk-m3 · bk) (1-m3) (1-bk)]       · (1-y3 + y3 · GsY) · (1-bk + bk · GsBK)                                                   ............ (107)   [1-y2 + y2.BsY-kY.y2 (1-y2)]     = (1-c3 + c3 · Bsc) · (1-m3 + m3 · BsM)       [[1-y3 + y3.BsY-ky] (y3 + bk-y3.bk)       (1-y3) (1-bk)] · (1-bk + bk · BsBK)                                                   ............ (108)

The meanings of the symbols in the formulas (106) to (108) are as follows. In addition, the above formulas (106) to
In (108), for example, in equation (106):
When obtaining c2 → c3, (m3, y
Since the expression (3) is included, the operation of the expression must be devised. The operation method of the expressions (106) to (108) is as follows.

1) Rsc, RsM, RsY, RsBK: C,
R filter light reflectance of solid print of each ink of M, Y, BK (black). 2) Gsc, GsM, GsY, GsBK: C, M, Y, BK
G filter light reflectance of solid print of each ink of (black). 3) Bsc, BsM, BsY, BsBK: C, M, Y, BK
B filter light reflectance of solid print of each ink of (black). 4) kc, km, kY: correction coefficients of the correction function of the ODG effect for each color plate. 5) In the equation (106), to find c3, it is necessary to use the unknown number (m3, y3).
Using (m2, y2) obtained from (105), c3
Find the value. 6) In the expression (107), to obtain m3, the expression (1)
M3 is obtained using c3 obtained from the above (06) and y2 obtained from the above equation (105) as the unknown y3. 7) In the equation (108), to obtain y3, the equation (1)
06) and (c3, m3) obtained from Expression (107), and the y3 value is obtained.

In the present invention, (c3, m3, y
The method of obtaining 3) is based on the C version, that is, the equation (1)
06) is performed as a starting point. In the present invention, it goes without saying that the image formation may be performed not on the basis of the C plate but on the basis of another color plate, for example, the M plate or the Y plate.

Next, a specific method for obtaining (c3, m3, y3) from the equations (106) to (108) will be described. The expressions (106) to (108) are, for example, the expression (106) relating to the C plate, when rearranged with respect to (c3), become a quadratic equation relating to (c3) as shown in the following expression (106-1).

Kc · (c3) ² + (Rsc−kc−1) · (c3) +1 − ｛[1-c2 + c2 · Rsc−kc · c2 (1-c2)] / [(1-m2 + m 2 · RsM) (1-y2 + y2 · RsY) (1-bk + bk · RsBK)]｝ (106-1)

The quadratic equation (106) for (C3)
Assuming that -1) is t (c3) ² + u (c3) + v = 0, the solution (c3) is given by the following equation (106-2). (C3) = [− u− ◆ u ² −4tv)] / (2t) (106-2)

As described above, in the present invention, (c
3) can be obtained. (M3) and (y3) can be similarly obtained.

C obtained by the above equations (106) to (108)
(C3) value for plate, (m3) value for M plate, (y
3) The value is obtained by performing multi-color printing (by performing four-color multiplex printing) under the (bk value) of a given black plate (BK plate), so that the ODG effect correction process as well as the inking process can be rationalized. (Halftone dot% value) of each color plate (C, M, Y plate) that is performed efficiently and guarantees a high degree of color (color) matching. That is,
The dot area ratio (c) of each color plate (C, M, Y, BK plate)
3, m3, y3, bk) are gradation proportional compression processing, gray balance processing, inking processing using a given black plate (BK plate), masking processing, and ODG effect correction processing. , And a final dot area ratio (c, m, y, b) for producing a four-color halftone print in which color consistency (color consistency) is highly guaranteed.
k).

As is apparent from the above description, the present invention rationalizes the inking process, which was difficult in the prior art, and the ODG, which was particularly difficult to perform quantitative processing in the dot gain (DG). (Optical dot gain) effect correction. According to still another feature of the present invention, the present invention relates to a dot gain (DG), which is an increase in halftone dot phenomenon during a printing process by another printing machine, that is, an MDG (mechanical dot gain). ) The effect correction processing can be rationally dealt with.

The above-described MDG effect can be easily corrected as compared with the ODG if the printing operation conditions of a printing machine or the like are stable. Hereinafter, M
A method for correcting the DG effect will be described. According to the present invention, the correction of the MDG effect at the time of the printing process by the printing press is performed for each of the color plates (C, M, Y, and BK plates) using the following formula (10).
9) to MDc, MDM, MDY, M shown in (112)
The idea is that it can be reasonably corrected by a quadratic equation with a correction coefficient of DBK. Note that the following correction coefficients for correcting the MDG effect such as MDc can be easily obtained from printing practice.

[0167]     c ′ = c3−MDc · c3 (1-c3) (109)     m ′ = m3−MDM · m3 (1−m3) (110)     y ′ = y3-MDY · y3 (1-y3) (111)     bk ′ = bk−MDBK · bk (1−bk) (112)

Each color plate (C, M,
Halftone dot area ratio (c ′, m ′, y ′, bk)
') Rationally performs gradation proportional compression processing, gray balance processing, masking processing, ODG and MDG effect correction processing (that is, correction processing for all DG effects), and has a high degree of color matching (color consistency). 4) is guaranteed
It can be used as a final dot area ratio (c, m, y, bk) for producing a color dot print.

As described above, the color matching (color co
The final dot area ratio (c, m, y, bk) for producing a four-color (C / M / Y / BK) color dot print with guaranteed nsistency is derived. In the present invention, the “printing color” of the color halftone print manufactured by multicolor printing using the final halftone dot area ratio (c, m, y, bk) is expressed by the following formula (113). Formulated as (115). Therefore, the following equations (113) to (115) make it possible to easily evaluate (verify) the color match between the color original and the color halftone print.

The following equations (113) to (115) can be obtained as follows. That is, formulas (113) to (11) relating to the light reflectance “R, G, B” of the manufactured color halftone print using the “print color” R, G, B filters measured.
5) is: Pollak's equation (2), theoretical equation (7) for predicting the color density of the single-color printed matter of the present invention, and correction term (2) for correcting the ODG effect of item C of the present invention. Theoretical formula (1) incorporating the following formula) into Pollak's formula (2)
3), the theoretical equation (14) for the M term, and the theoretical equation (15) for the Y term. Note that the following expressions (113) to (1)
In 15), Rp, Gp, and Bp are the light reflectances of the paper (printed paper) viewed through the R, G, and B filters, respectively.

[0171]   R = Rp. [1-c + c.Rsc-kc. (C + bk-c.bk) (1-c) (1-bk)] · (1-m + m · RsM) (1-y + y · RsY) (1-bk + b k · RsBK) ............ (113)   G = Gp · (1-c + c · Gsc) [1-m + m · GsM-km (m + bk-m .Bk) (1-m) (1-bk)]. (1-y + yGsY) (1-bk + bk ・ GsBK) …………… (114)   B = Bp. (1-c + c.Bsc) (1-m + m.BsM) [1-y + y.B sY-ky. (y + bk-y.bk) (1-y) (1-bk)] (1-bk + bk ・ BsBK) ……………… (115)

According to the above-described procedure (method) of the present invention, 1) a continuous-tone color original is proportionally compressed to a halftone dot tone, 2) a gray balance process is performed, and 3) a masking process is performed. 4). The ODG effect is corrected in the overprinted state. 5). The inking (GCR, UCR, UCA) is also rationally processed. 6). The MDG effect on the printing press. Correction is also rationally processed, and four-color (C, M, Y, BK) overprinting is performed to produce high-quality, especially four-color halftone prints with highly guaranteed color matching. You.

As is evident from the above, the present invention provides a next-generation color separation apparatus (color scanner) strongly demanded by the color printing industry, and a highly skillless (amateur) scanner. (A foolproof scan
ner) and push-butt color (push-butt)
This is extremely useful in realizing the production of a four-color halftone print image in which a high degree of color matching is assured by on-color.

[0174]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in further detail below with reference to an embodiment relating to a method of producing a four-color (C, M, Y, BK) halftone dot printed image using a given black plate (BK plate). .
In other words, in four-color (C, M, Y, BK) multicolor plate making,
Tone conversion processing (gradation proportional compression processing), gray balance processing, masking processing, inking processing (GCR, UC
R, UCA) and dot gain (DG) processing (OD
G, MDG) and color matching (color
4 colors (C, M, Y, BK) with guaranteed consistency
1 shows an embodiment of the invention for producing a color dot printed image.

In the present invention, as described above, these various processes are rationally performed by operating related theoretical formulas. For this reason, first, the theoretical formulas to be employed and the operation conditions (parameter values) thereof are arranged.

1. Theoretical formula to be used: (1). First formula: This is a theoretical formula for executing the gray balance process and the gradation proportional compression process, and is expressed by formulas (100) to (1).
02) and equations (100-1) to (102-1). (2) Second formula: This is a theoretical formula for executing the inking process, and employs formulas (103) to (105). (3) Third formula: This is a theoretical formula for executing masking (color correction) processing, and employs formulas (106) to (108). (4). Theoretical formula (109) for correcting a mechanical dot gain (MDG) effect brought about when printing (printing) by a printing machine in DG (dot gain) processing.
(112) is not adopted. This is because the MDG at the time of printing by the printing press can be stabilized according to the operating conditions of the printing press, and handling is easy. (5). Relational expression of adopted black plate (BK plate): given black plate (B
As the (K-version) curve, a curve represented by a linear equation represented by bk = α (x−β) was employed. Where x is min (c
1, m1, y1).

[0177] 3. Regarding parameter values in each theoretical formula: The parameter values used in each theoretical formula are as follows. (A). Halftone dot area% preset for the H / S part of the C, M, and Y plates
Value: AHc 0.01 / Asc 0.95 AHM 0.01 / AsM 0.95 AHY 0.01 / AsY 0.95 (b). Density value of solid portion of C / M / Y ink (Ds): Dsc 1.39 Dsm 1.35 Dsy 1.27 (c). Yule-Nielsen coefficient: nc 2.2 nm 1.8 ny 1.8 (Note) The Yule-Nielsen coefficient ,
That is, the value of (nc, nm, ny) is calculated by the equation (100a),
This is used as a value that defines the γ value of the equations (100) to (102). Further, the Yule-Nielsen coefficient is defined by Expression (4). However, in the present invention, this Yule
The value of the Nielsen coefficient (nc, nm, ny) is given by equation (4)
It should be noted that it is not limited to the values defined in. (D) C / M / Y / B viewed through R / G / B filter
Optical reflectance (R) of solid portion of K ink: Rsc 0.04 / Gsc 0.37 / Bsc 0.65 RsM 0.85 / GsM 0.05 / BsM 0.29 Rsy 0.95 / GsY 0.93 / BsY 0.05 RsBK 0.04 / GsBK 0.04 / BsBK 0.04 (E). Optical A correction coefficient (kc, k) of a correction formula (quadratic formula) for correcting the dot gain (ODG) effect
M, kY): kc 0.7 / km 0.55 / ky 0.52 (f). Reflectance of printing paper (Rp) In the operation of the theoretical formula, the reflectance (Rp) of printing paper was treated as 1. . (G) Image information obtained through the R / G / B filter (x
c, xM, xY): These image information (xc, xM, xY)
Used a normalized light intensity value (a value obtained by adjusting the dynamic range to 0 to 1).

(Example 1) A color film manuscript (FUJI SCANNER FILM KIT) was prepared in the following procedure.
Was processed to produce a color proof (color proof). (1) Color scanner “ISOM” manufactured by ISOMET, USA
According to ET 405 ", a color film original is converted to R / G /
R / G / B data was obtained by color separation in B mode. In the operation of the ISOMET 405 scanner,
The setup was set up to cover the entire range of the color film original in order to receive accurate image information from the color film original. (2). R / G / B Tiff D thus received
ATA is calculated by software that can be processed by various theoretical formulas of the present invention, and C / M / Y / BKTiff DA
Converted to TA. (3) Next, for general DTP output work, the C
/ M / Y / BK data was converted to Postscript DATA.
As the RIP process, AGFA's Tipan RIP was used. (4) A proof (color proof) was created using the Poststcipt DATA. Note that AGFA is used as the output device.
C / M / Y using "Imagesetter Phoenix"
Film output was performed for each color of / BK. (5) Next, a proof (color proof) was prepared by a press match dry proof printing system (pre-proof system) manufactured by AGFA. That is, each color sheet output as a film is stuck on the backing paper by the AGFA laminator,
Exposure was performed with a bright room printer MUTILIGHT8010R to produce a color proof (color proof). In parallel, a printing plate was produced using the output color films, and a four-color halftone print was prepared.

In Example 1, the given black plate (BK plate)
That is, the black plate (BK) defined by the equation (100b)
Skeleton black defined by bk = 2.0 (x−0.5) was used as the plate. Table 3 below shows the final solution (c, m, y, bk) calculated by the calculation software (where bk is given). FIG. 16 shows the final solution. FIG. 16 is called a color separation curve. (Note) In Table 3, saturation (c = 42%) is observed in the halftone dot area ratio (c) of the C plate for the following reason. In GCR, all colors (colors) are expressed by two kinds of color inks and BK ink. Therefore, in the calculation of the theoretical formula of the present invention, the calculation was performed with the upper limit of the dot area ratio of the color ink set to 200%. In this regard, step NO. 22, the total dot area ratio of the color ink was 20.
It is set to 0%.

[0180]

[Table 3]

When a color proof (proof) was prepared based on the above theoretical data, the color quality of the color proof (proof) was extremely excellent. That is, the color proof printing (proof) was a highly reproduced color (color) of a color original in the entire dynamic range of the HS section. In addition, it is possible to produce a color halftone print image with high color matching under UCA processing for the purpose by setting the parameters of each theoretical formula and the settings of the functional formula that defines the black plate (BK plate). We could verify what we could do.

(Example 2) Color film original (the U
Same as the CA processing route. ) To produce a color proof (color proof) is described in the first embodiment.
Is exactly the same.

In Example 2, the given black plate (BK plate)
That is, the black plate (BK) defined by the equation (100b)
As the plate, a full black defined by bk = 0.99 (x-0.01) was used. Table 4 below shows the final solution (c, m, y, bk) calculated by the calculation software (where b
k is given). FIG. 17 shows the final solution. FIG. 17 is called a color separation curve.

[0184]

[Table 4]

When a color proof (proof) was prepared based on the theoretical data described above, the color consistency (color consistency) was sufficiently satisfactory. In addition, the setting contents of the parameters of each theoretical formula, black plate (B
R version), depending on the setting of the function formula
It was also verified that a color halftone print having high color matching can be produced under the CR process. Furthermore, Embodiments 1 and 2 reflect plate-making practice in which the setting conditions of the black plate (BK plate) are changed while using the same color film manuscript. However, the results of these embodiments are completely the same. And showed satisfactory color matching in both cases. This means that, regardless of the setting conditions of the black plate (BK plate), four-color halftone prints of the same quality and high color matching are produced by the present invention. .

[0186]

According to the present invention, the following excellent effects can be obtained. 1. When reproducing the color (color) of a continuous tone color original as a four-tone (C, M, Y, BK) halftone print image of halftone, 1). Color matching (color consistency; co
Ink processing (GCR, UCR, UCA) and dot gain (dot gain, optical and physical halftone dot thickening) correction processing (ODG, MDG), which are extremely important for ensuring lor consistency, are performed. (2). Each color plate (C, M, Y version) and black plate (BK
Because the tone conversion process (gradation proportional compression process), gray balance process, and masking (color correction) process, which are extremely important in color reproduction by multi-color printing of the color plate, are reasonably quantified, Because all the elemental technologies for producing 4-color halftone print images are rationally quantified and processed, high-quality 4 colors with high color consistency (color consistency) are highly guaranteed. Color halftone printed images can be produced. The important processing techniques (main elemental techniques in color reproduction) described above when producing a 2.4-color halftone print image are as follows:
As described above, the method of rationally quantifying and processing all is adopted, so that a high-quality four-color halftone dot printed image can be manufactured under automation and skimming. 3. Digital image processing techniques related to the production of four-color halftone print images these days involve local (local) processing, opacity in the theory, and processing of the entire image formed as a sum of each pixel. It is completely inadequate when evaluated from the viewpoint of organic relevance. In this regard, in the color reproduction technology of the present invention, since all the element (core) technologies are quantified by theoretical formulas (functional formulas), the theory is transparent, harmonized with the total sum, and It can be operated on purpose. In the technology of producing a 4.4-color color halftone print image, considering that color (color) reproduction is performed by coating (applying) color ink on halftone dots (dot area ratio) of each pixel, The entire manufacturing technology (a collection of elemental technologies) should be assembled from the viewpoint of how the main character “dot” is quantitatively defined from beginning to end. In view of the above, the present invention provides a four-color halftone print image with a "dot (dot)" which is not seen in the past.
The present invention provides a total digital processing technology in which each elemental technology is unified with "t)" as a hero, and its industrial utility value is extremely large.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining the dot gain phenomenon (Dot Gain).

FIG. 2 is a diagram for explaining the degree of coincidence between an actually measured value of ODG (optical dot gain) and various theoretical values in a C-plate.

FIG. 3 is a diagram for explaining the degree of coincidence between an actually measured value of ODG (optical dot gain) and various theoretical values in the M plate.

FIG. 4 is a diagram illustrating the degree of coincidence between an actually measured value of ODG (optical dot gain) and various theoretical values in the Y plane.

FIG. 5 is a diagram illustrating the degree of coincidence between an actually measured ODG (optical dot gain) value and various theoretical values in the BK plane.

FIG. 6 is a diagram showing a concept for quantifying (formulating) a correction term for correcting the ODG effect of the C plate under the use of the BK plate of the present invention.

FIG. 7 is a diagram showing the effectiveness of introducing the ODG correction term of the present invention into Pollak's equation (2) evaluated by R filter light reflectance.

FIG. 8 is a diagram showing the effectiveness of introducing the ODG correction term of the present invention into Pollak's equation (2) evaluated by G filter light reflectance.

FIG. 9 is a diagram showing the effectiveness of introducing the ODG correction term of the present invention into Pollak's equation (2) evaluated using the B filter light reflectance.

FIG. 10 shows the spectral reflectance (λ = 450n) of the C plate.
FIG. 9 is a diagram for explaining the degree of coincidence between the measured value of ODG evaluated in m) and the correction term of the present invention.

FIG. 11 is a spectral correction coefficient (kλ) employed in the ODG correction term (second-order correction function) of the present invention in the form of a spectral reflectance.
FIG.

FIG. 12 is a diagram showing the degree of coincidence between the spectral correction coefficient (kcλ) of the present invention and the correction coefficient (1-Rcλ) of the Rogers theoretical formula with respect to the spectral correction coefficient (kλ) in the C version.

FIG. 13 shows the actual measured value of ODG evaluated by the spectral reflectance, Po
The theoretical value of the llak formula (16) and the theoretical formula (1
It is a figure which shows the theoretical value by 8).

FIG. 14 is a diagram showing the validity of various theoretical formulas for correcting the ODG effect and the theoretical formula of the present invention evaluated by the color difference (ΔE) of printed matter.

FIG. 15 is a diagram illustrating an example of a preset tone curve of a black plate (BK plate).

FIG. 16 is a diagram showing an example of a color separation curve (c, m, y, bk) of the present invention that guarantees high color matching.

FIG. 17 is a diagram showing another example of the color separation curve (c, m, y, bk) of the present invention that guarantees high color matching.

Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI H04N 1/60 H04N 1/46 Z (56) References JP-A-11-88694 (JP, A) JP-A-9-26663 (JP, A) JP-A-7-222005 (JP, A) JP-A-4-248767 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B41C 1/00 B41J 2/525 G06T 1 / 00 510 H04N 1/405 H04N 1/46 H04N 1/60 G03F 3/08

Claims (6)

(57) [Claims] 1. Using R, G, B system image information (xc, xM, xY) of each pixel of a color original, (i) gradation compression processing of each pixel, and (ii) equally absorbed in each pixel. R, G,
A predetermined amount of the gray (black) component of the B-series image information
And (iii) masking processing for adjusting the improper absorption of printing ink based on the correction amount of the dot gain (DG) effect and the amount of the inking processing, and the color of the color original is performed. The halftone dot area ratio (c, m, y, BK) of each color plate (C, M, Y, BK plate) capable of producing a C, M, Y, BK system four-color halftone print image with excellent reproducibility. b
In the method for setting k), (i) the proportional compression processing of the gradation is performed by the following equations (100) to (1).
02), the R, G, B system image information (x
c, xM, xY) to determine the halftone dot area ratio (c1, m1, y1) of each of the C, M, and Y color plates. (ii). The predetermined amount of the gray (black) component of the R, G, B system image information equally absorbed in each pixel is set to the black version (BK version)
When replacing with the above, the predetermined amount of the gray (black) component is set to a halftone dot area ratio (bk) obtained by a predetermined black plate function, and (ii) -2. Each color plate after inking. The dot area ratio (c2, m2, y2) of the (C, M, Y version) is calculated by the following equations (103) to (10).
(Iii). The masking process is performed according to the following equations (106) to (10).
8), the dot area ratio (bk) of the given black plate (BK plate) and the (c2, m2, y2) are used to obtain (c
(Iv). (Iv). The above (c3, m3, y3) and a given (bk) are used as a final halftone dot area ratio (c, m, y, bk). C, which is excellent in color reproducibility of a color original,
A method of setting a dot area ratio (c, m, y, bk) of each color plate (C, M, Y, BK plate) capable of producing a four-color M, Y, BK halftone print image. 1. Formulas (100) to (102): c1 = AHc + [(1-10− ^{γ · xc} ) / (1-10− ^γ )] · (Asc−AHc) (100) m1 = AHM + [(1-10− ^{γ · xM} ) / (1-10− ^γ )] · (AsM−AHM) (101) y1 = AHY + [(1-10− ^{γ · xY} ) / ( 1-10 ^-γ )] · (AsY−AHY) (102) where the symbols in the formulas (100) to (102) mean the following. The expression (100) for the C color plate will be described, and the description for the other color plates (M, Y) will be omitted because of similarity. 1) c1: Halftone dot area ratio at an arbitrary pixel point of the C plane image. 2) xc: Image information obtained through an R filter of a color original. Note that xM and xY are a G filter and a B filter, respectively.
5 shows image information obtained through a filter. 3) AHc: The halftone dot area ratio set in the H portion (lightest portion) of the C-plate image. 4) Asc: The dot area ratio set in the S portion (darkest portion) of the C-plate image. 5) γ: any coefficient including Dsc / nc. However, Ds
c is a solid density value of the C-plate image, and nc is a Yule-Nielsen coefficient, and these are R filter light reflectance (R
c) and the relational expression (Yule-Nielsen equation) R of the dot area ratio (c)
c = (1−c + c · 10− ^{Dsc / nc} ) ^nc is established. 2. Expressions (103) to (105): c2 = (c1-bk) / (1-bk) (103) m2 = (m1-bk) / (1-bk) (104) y2 = (y1-bk) / (1-bk) (105) Formulas (106) to (108): 1−c2 + c2 · Rsc−kc · c2 (1−c2) = [1−c3 + c3 · Rsc−kc · (c3 + bk−c3 · bk) (1−c3) (1−bk) ] (1-m3 + m3 * RsM) * (1-y3 + y3 * RsY) * (1-bk + bk * RsBK) (106) 1-m2 + m2 * GsM-km * m2 (1-m2) = (1-m2) 1-c3 + c3 · Gsc) · [1-m3 + m3 · GsM-km · (m3 + bk-m3 · bk) (1-m3) (1-bk)] · (1-y3 + y3 · GsY) · (1-bk + bk · GsBK) (107) 1−y2 + y2 · BsY−kY · y2 (1−y2) = (1−c3 + c3 · Bsc) · (1−m3 + m3 · BsM) · [1−y3 + y3 · BsY−kY · ( y3 + bk−y3 · bk) (1-y3 ) (1-bk)] · (1-bk + bk · BsBK) (108) where the meanings of the symbols in the equations (106) to (108) and the operation of the equations are as follows. The description of symbols having similarity is omitted. 1) kc: a correction coefficient of c1 (1-c1), which is an ODG correction function (quadratic expression) for correcting an optical dot gain (ODG) effect in a C-color monochrome image. 2) Rsc, RsM, RsY, RsBK: C, M, Y, B
Each R filter light reflectance of K solid print. 3) Gsc, GsM, GsY, GsBK: C, M, Y, B
Each G filter light reflectance of K solid print. 4) Bsc, BsM, BsY, BsBK: C, M, Y, B
Each B filter light reflectance of the K solid print. 5) In the equation (106), c3 is obtained using m2 and y2 as the unknowns m3 and y3. 6) In equation (107), c obtained from equation (106)
3, and using the above y2 as the unknown y3, m
Ask for 3. 7) In equation (108), c obtained from equation (106)
3, and y3 is obtained using m3 obtained from Expression (107). 2. R, G, B system image information (xc, xM, x
Y) is calculated by the following equation (100-
The halftone dot area ratio (c, m, y, b) according to claim 1, wherein a value determined by (1) to (102-1) is adopted.
k) How to set. xc = xc '... (100-1) xM = (Dsc / DsM) / xM' ... (101-1) xY = (Dsc / DsY) / xY '... (102-1) However, in formulas (100-1) to (102-1),
(Xc ′, xM ′, xY ′) are R, G, B system image information (xc, xM, xY) before gray balance processing, respectively. 3. The halftone dot area ratio (b) of a given black plate (BK plate)
2. The halftone dot area ratio (c, m, y, bk) according to claim 1, wherein k) is given by a linear expression of the following expression (100b).
How to set. bk = p (x−q) (100b) where x is R, G, which is equally absorbed in each pixel.
The amount of the gray (black) component of the B image information, that is, the minimum (mi)
n) shows min (c1, m1, y1). Also, p>
0 and q are 0 (zero) or q> 0. 4. A dot area ratio (b) of a given black plate (BK plate)
2. The method for setting a dot area ratio (c, m, y, bk) according to claim 1, wherein k) is given by the following equation (100c). bk = AHBK + [(1−10− ^{γ · xBK} ) / (1−10− ^γ )] · (AsBK−AHBK) (100c) where xBK is R, G, and B image information ( xc, xM, x
Y). Also, AHBK
And AsBK indicate the dot area ratios set respectively at the start point (SP) and the end point (EP) of the black plate. 5. R, G, B pixel information (xc, xM, x
2. The method of setting a dot area ratio (c, m, y, bk) according to claim 1, wherein Y) is a normalized light amount value. 6. A mechanical dot gain (MDG)
Each color plate (C, M, Y, BK plate) to correct the effect
As the dot area ratio (c, m, y, bk) of
The halftone dot area ratio (c, m, y, bk) according to claim 1, wherein the numerical values shown in 9) to (112) are used.
How to set. c ′ = c3-MDc · c3 (1-c3) (109) m ′ = m3-MDM · m3 (1-m3) (110) y ′ = y3-MDY · y3 (1) −y3)... (111) bk ′ = bk−MDBK · bk (1−bk)... (112) where MDc, MDM, MDY, and MDBK are mechanical
The coefficients of the correction function (quadratic equation) of each color plane (C, M, Y, BK plane) for correcting the dot gain (MDG) effect are shown.