JPH03202978A - Color reproduction prediction method related to xyz value of dot halftone picture - Google Patents

Abstract

PURPOSE:To automate the prediction of color reproduction quality by predicting color reproduction related to the CIE standard color specification system three simulation values X, Y, Z values of the transmission light of an ink film layer and each tone reproduction related to the XYZ value of a system consisting of a single color ink film layer and its supporting body from the combination of the value of the dot area rate of each dot halftone picture. CONSTITUTION:A data is fetched into a processing system as a picture data 5 quantized to the dot area rate by a process scanner 1, and converted into a picture data 6 of a XYZ color specification system. In such a case, the color reproduction related to the CIE standard color specification system three stimulation values X, Y, Z values of the transmission light of the ink film layer of the dot halftone picture and the tone reproduction related to the XYZ value of the system consisting of the single color ink film layer and its supporting body, is predicted from the combination of the value of the dot area rate of each color of the halftone picture with reproduction to be predicted. Thus, the XYZ value of the reproduced color can be accurately predicted from the value of the dot area rate of each color of the dot halftone picture without relying on the experience and eye measurement of an operator, and the prediction evaluation of the color reproduction quality can be automated.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application] The present invention relates to a method for predicting color reproduction regarding the XYZ values of halftone halftone images, and more specifically to a method for predicting reproduced colors of a printed image after color separation in a plate-making process, etc. , relates to a method for evaluating.

[Prior Art] Conventionally, in the plate-making color separation process, a method for predicting the color reproduction of a color separation image is that a color separation worker grasps the relationship with the proof from experience and calculates the dot area ratio and reproduction of each color. The general method is to predict the relationship between colors, and therefore the color reproduction evaluation of color separated images also relies heavily on the operator's experience and visual measurements. After obtaining the color, the only option is to measure it with a spectrophotometer or colorimeter, and in practical terms, this method of predicting and confirming color reproduction is meaningless and has never been attempted.

[Problem to be solved by the invention] As described above, technology for accurately predicting the reproduced colors of a color separated image without relying on the operator's experience or visual estimation is extremely important from the perspective of automating the prediction of color reproduction quality. Despite this, it has not been done to date.

Therefore, the present invention was made in view of the above-mentioned conventional problems.
The purpose of the present invention is to provide a color reproduction prediction method regarding the XYZ values of a halftone halftone image, which enables accurate prediction of reproduced colors without relying on operator experience or visual estimation, and enables automation of prediction of color reproduction quality. .

[Means for Solving the Problems] In order to achieve the above object, the color reproduction prediction method of the present invention includes the following:
The CIE standard color system tristimulus values X, Y of the transmitted light of the ink film layer of the halftone halftone image are calculated from the combination of the values of the halftone area ratio of each color of the halftone halftone image whose color reproduction is to be predicted.
, means for predicting color reproduction regarding Z value (hereinafter simply referred to as CI EXYZ or XYZ value), and monochromatic ink g
The structure includes means for predicting gradation reproduction regarding the XYZ values of the system consisting of the I layer and its support.

Further, the present invention provides a means for predicting the color reproduction of transmitted light, in which the probabilistic area for all combinations of overlapping combinations of each color ink and the color reproduction value at an area ratio of 1.0 are used as variables to comprehensively predict the color reproduction of transmitted light. This is a structure that predicts color reproduction regarding the XYZ values of transmitted light.

Further, the present invention provides, in the means for predicting gradation reproduction,
The configuration is such that gradation reproduction is predicted as the sum of diffusion, transmission, reflection, etc. on the optical path from the incidence of the irradiation light on the halftone image to the exit side.

Still further, in the present invention, the absorption value of the ink film layer in the gradation reproduction prediction means is obtained from the predicted value obtained by the transmitted light color reproduction prediction means.

In the present invention, the standard color system tristimulus defined by CIE (Commission Internationale de l'Eclairage) of the reproduced color is determined from the combination of values of the halftone area ratio of each color of the halftone image whose color reproduction is to be predicted. By accurately predicting the values x, y, and z, it is possible to accurately predict and evaluate the specific reproduced color of a halftone halftone image after color separation that is applied to the platemaking process at that color separation process stage. I can do it. Therefore, there is no need to rely on the experience or visual estimation of a color separation operator, and it is possible to automate the pre-8i evaluation of color reproduction quality. In other words, based on signals or data regarding the dot area ratio, reproduced colors can be calculated in real-time on-fin without printing out proofs or film.
It becomes possible to make predictions regarding the total color system (IEXYZ or more).

Hereinafter, the configuration of the present invention will be explained in more detail.

According to the present invention, the color reproduction regarding the XYZ values of the transmitted light of the ink l'1 layer of the halftone image is calculated from the combination of the values of the halftone area ratio of each color of the halftone image. "Means for predicting" means to predict the ink film from the combination of the halftone area ratio of each color. T le? h
Pass (7) X/Xo, Y/Yo,
This is a means of predicting Z/Zo. cyan, magenta,
To explain an example of a halftone dot image consisting of four colors of yellow and black, for X/Xo, T (X/Xo) = f 1 (C, M, Y, K).
It can be predicted by the following relationship. Here, T(
X/Xo) is the transmittance, and C, M, and Y are the positive halftone dot area ratios of each ink of cyan, magenta, yellow, and black. To give a concrete example of the relationship fl, T (X/Xo) = (1-C) (1-H) (1-Y
) (to 1-)Tbase (X/Xo)+C(1-H
)(1-Y)(1-K)Tc(X/Xo)+(1-
C) M(1-Y)(1-K)Tl(X/Xo)+
(1-C) (1-H)Y (1-to)Ty (X/Xo
)+(1-CHI-H)(1-Y)KTk (X/X
o )+0M(1-Y)(1-K)Tcm(X/Xo
)+c(i-H)Y(1-K)TCV (X/X.

-+-C(1-H)(1-Y)KTck (X/X.

+(1-C)MY(1-K)TmV (X/X.

+(1-C)M(1-Y)KTmk (X/X.

+(1-C)(1-H)YKTCm (X/X.

+CMY(1-)TcmV (X/Xo)+(1-
C) MYKTmyk (X/Xo)+C(1-H)Y
KTVkC(X/Xo)+0M(1-Y)KTkcm
(X/Xo)+CMYKTCIIIVk (X/X
o ) −(1) (Neugebauer formula) It can be predicted by the following.

Here, Tc (X/Xo), -, Tcmyk (X
/Xo) is the actual value of X/Xo of the peta ink film when the ink combination is C2..., CMYK. Also, T
base (X / X o ) is ×/x of the non-printing area
The value of O is theoretically T base = 1.0.

Based on a similar relationship, Y/Yo and Z/Zo can also be predicted from the combination of dot area ratio values.

Note that the relationship shown in (1) is the color reproduction regarding the XYZ values of the overall transmitted light, with the probabilistic area for all combinations of overlapping combinations of each color ink and the color reproduction value at the area ratio of 1 and 0 as variables. It is a prediction.

On the other hand, "means for predicting gradation reproduction regarding XYZ values of a system consisting of a monochromatic ink film layer and its support" in the present invention
are X/Xo, Y/ of the reflection of a monochromatic halftone image.
It is a means to predict Yo, Z/Zo, and X/X
Taking o as an example, R(X/Xo) = f 2 (T+
, -, Tn, R+, -, Rn). Here, R(X/Xo
) is the reflectance, and T1-, Tn, R+... Rn is the transmittance or reflectance in transmission and reflection, which are elements on the model. Without giving a concrete example of the relationship f2, R(X/Xo)=f2 (t, r, x, s, K)...
...(2) Here, K is the reflectance on the surface of the printed image, i-s is the permeability in the paper, r is the reflectance in the paper, and X is the paper or ink film in the optical path from the paper or ink film. , a is the halftone area ratio of the halftone image, [ is the ink film transmission X/Xo, t
o is the transmission of X/X o in the non-printing area, and usually to
= i, o. In addition, the index n is theoretically n=
Takes a value of 2.0.

Using similar relationships, predictions can also be made for Y/Yo and Z/Zo.

The relationship shown in (2) predicts gradation reproduction as the sum total of transmission and reflection on the optical path from the incidence of the irradiation light to the exit side of the halftone image.

The color reproduction prediction method of the present invention is characterized by comprising the above-mentioned transmitted light color reproduction prediction means and tone reproduction prediction means, and for X/Xo, R(X/Xo)-f2
(T+, ・=, f 1 (C, M, Y, K)
.

・Jn, R+, ・pn) It can be predicted by the relationship. Above (1)
, (2) can be predicted as... (3). At this time (1-a)=(1
-CHI-H)(1-Y)(1-Kl, tO=T
This will be the base.

That is, the absorption value of the ink film layer in the gradation reproduction prediction means is obtained from the predicted value obtained by the transmitted light color reproduction prediction means.

As described above, from the combination of the values of the halftone dot area ratio of each color of the halftone image, the reproduced color X/Xo,
The values of Y/Yo and Z/Zo can be predicted. J
XO according to ISZ8722 etc.

Since Yo and Zo can be found, for example, CIE D65
Taking a light source as an example, X= 95.02 R(X/Xo)Y= 100
．． OR(Y/Yo) Z=108.8 R(Z/Zo).

Also, CIELAB or L derived from CIEXYZ
The HC color system is a psychophysical quantity based on colorimetry.
se l It is said to be a good approximation of a one-color solid, and is used for color conversion and
It has been recognized that it is advantageous in application to color correction and color reproduction evaluation.

In addition, Shi*a*b*, L*u V*, etc. are JISZ 87
29 etc., and the color difference ΔE is obtained in the same manner.

Δ1. ．． Δa, Δb, ΔU, ΔV etc. are JIS
It can be determined using Z8730.

Conversion to [Pro°C*] is possible using the following equation, and thereby the reproduced color based on the combination of dot area ratios of CMYK inks can be specified on the pseudo-Munsel one-color solid.

Bi = Bi] 1° = tan ” (b ” /a ”)bo-””
+ b ''') 1/2 Next, an apparatus for executing the color reproduction prediction method of the present invention will be described.

FIG. 1 is a block diagram showing an example of an apparatus for executing the color reproduction prediction method of the present invention, in which 1 is a plate making scanner, 2
indicates CPIJ, 3 indicates display, and 4 indicates mouse. The image data 5 quantized to a halftone dot area ratio is taken into the processing system from the plate making scanner 1, and converted into image data 6 in the XYZ color system according to the method of the present invention. Similarly, it is further converted to another color space (for example, image data 7 of L*a2b'' system). Note that 5, 6, and 7 may be disks or buffers.

FIG. 2 is a block diagram showing another example of a device for executing the color reproduction prediction method of the present invention, in which transmitted light from a light source 9 of a photographic original 8 is received by a device such as an optical fiber 10, Image data in the XYZ color system is displayed on an XYZ value meter 14 via a color calculation circuit 11, a dot area ratio meter 12, and a dot area ratio-XYZ value converter 13. Similarly, it is also possible to convert and display image data in another color space.

[Example] The present invention will be explained in more detail below by showing examples of the present invention.

In the prediction means of the present invention, if n=2 in the above (3), then... (4) Here, K, r, s, and x are parameters that differ depending on the paper, ink, etc. used. , it is necessary to actually measure it. (1
-a) is the area ratio of the non-printing area, (1-a) = (1-
C) (1-H) (1-Y) (1-K). Further, T is the transmittance of light transmitted through the ink film, and can be predicted using the above-mentioned (1>).

In addition, in the above (1>), Tc,...T cmy
k is the transmittance X/Xo, Y/Yo, Z/Zo of the peta ink film when the ink combination C1..., CMYK is used, but since this varies depending on the ink used and the printing conditions, it is necessary to actually measure it.

Therefore, it is necessary to actually measure and determine K, s, r, y, Tc, -, 1 cmyk in advance according to the applied printing conditions.

By the way, when the condition K j, t T → 0, 0,
There is no practical problem if the fouling rate of Y and Z lights is measured. Specifically, K can be estimated from the convergence value of the area ratio versus -QoaR curve as shown in FIG. Also, Tc...
, Tcmyk can also be obtained by measuring the transmittance of petain ink printed on a transparent film base, but since it is difficult to measure r, s, and x, they were determined by the following method.

That is, if α-rx(1-s) and β-r(1-x), then (4) becomes.

Here, if we consider monochromatic halftones under the condition that T is sufficiently large and (1-a) → 0.0, then ff1oa (R-K)=-4og (α [(1-a
)Tbase+Tko2)=-4ogα-2too
[(1-a)Tbase+T], -10g(R
-K) vs. -IlOgT and extrapolate the plot of the medium-high concentration region to -t10 (JT = 0.0) to obtain the value of -/lOgα (see Figure 4). Let n be the slope.

Furthermore, under the condition of a=0.0 (paper white), β-1(x to R- Then we get β.

Note that since the value of n usually takes a different value for each ink layer, TC, ..., Tcmyk (-Ti'
) Correct the value.

Table 2 In this example, n is black ink.

Each parameter was determined as described above, and the obtained values are shown in Table 2 in Cloth 1 below.

Table 1 According to these values, X/Xo, Y/Yo for approximately 850 color patches using the method of the invention.

When Z/Zo was predicted and correlated with the actual measured value on a logarithmic scale, the correlation coefficient for each stimulus value was X/Xo:R = 0.99
8(L, Y/Yo: R=0.9979,
Z/Zo:R=0.9975, and a good result was obtained.

[Effects of the Invention] As explained in detail above, according to the color reproduction prediction method of the present invention, the XYZ values of the reproduced color can be estimated from the value of the halftone area ratio of each color of the halftone image by the operator's experience. It is now possible to make accurate predictions without relying on color reproduction quality or visual measurements, and it has become possible to automate the predictive evaluation of color reproduction quality. Furthermore, it is now possible to predict reproduced colors in real time from dot area ratio data without having to print out proofs or film.

In particular, in today's world, it has become possible to quantize dot area ratios or convert color separation signals into data and process, manipulate, and analyze them using general-purpose computers and other numerical processing systems rather than plate-making scanners such as layout scanners.Automation of color reproduction quality prediction From this viewpoint, the significance of the present invention is great.

[Brief explanation of drawings]

FIGS. 1 and 2 are block diagrams showing an example of an apparatus for implementing the color reproduction prediction method of the present invention, and FIGS. 3 and 4 are area ratios obtained from actual measurements for determining parameters, respectively. vs. QoaR butt diagram and -1og
FIG. 2 is a plot of T vs. −1 oa (R−K).

Claims (4)

[Claims] (1) CIE standard color system tristimulus values X, Y of the transmitted light of the ink film layer of the halftone halftone image from the combination of halftone area ratio values of each color of the halftone halftone image whose color reproduction is to be predicted , relating to the XYZ values of a halftone halftone image, comprising means for predicting color reproduction regarding Z values and means for predicting gradation reproduction regarding XYZ values of a system consisting of a monochromatic ink film layer and its support. Color reproduction prediction method. (2) In the means for predicting the color reproduction of transmitted light, the probabilistic area for all combinations of overlapping combinations of each color ink and the color reproduction value at an area ratio of 1.0 are used as variables to calculate the overall transmission. 2. The method for predicting color reproduction regarding XYZ values of a halftone halftone image according to claim 1, further comprising predicting color reproduction regarding XYZ values of light. (3) In the means for predicting gradation reproduction, gradation reproduction is predicted as the sum of transmission and reflection on the optical path from the incidence of the irradiation light to the halftone image to the emission thereof. 2. A color reproduction prediction method regarding XYZ values of a halftone halftone image according to item 1. (4) The halftone image according to claim 1, wherein the absorption value of the ink film layer in the gradation reproduction prediction means is obtained from the predicted value obtained by the transmitted light color reproduction prediction means. A method for predicting color reproduction regarding XYZ values.