=Paper=
{{Paper
|id=Vol-2387/20190414
|storemode=property
|title=None
|pdfUrl=https://ceur-ws.org/Vol-2387/20190414.pdf
|volume=Vol-2387
|dblpUrl=https://dblp.org/rec/conf/icteri/ShovheniukKSSZ19
}}
==None==
https://ceur-ws.org/Vol-2387/20190414.pdf
Information Technology of Digital Images Processing
with Saving of Material Resources
Mykhailo Shovheniuk1 Bohdan Kovalskiy2
Mariia Semeniv2 Vitalii Semeniv2 Nataliia Zanko2
1 Institute for Condensed Matter Physics National Academy of Sciences of Ukraine, Lviv,
Ukraine
2 Ukrainian Academy of Printing, Lviv, Ukraine
mv@icmp.lviv.ua, bkovalskyy@gmail.com, krykmary17@gmail.com,
1986ministr@gmail.com, zankonatalya@gmail.com
Abstract. The authors proposed new information technology that is built on
representing original image in a new color space ICaS. We found the exact so-
lutions of equations for synthesis of color image, which allowed to optimize the
using of inks. The specialized software for processing digital originals by tradi-
tional and new technologies in the common information environment was de-
veloped. The software is based on a new color separation information model
developed by the authors. It is shown that the new technology works on analyti-
cal methods.
Keywords: information technology, color separation, autotype equation, spe-
cialized software, digital original, methods, models.
1 Introduction
A color space of digital originals is represented as RGB. Color gamut of RGB is de-
termined by its primaries: a set of the emitters. Whereas the primaries of printing
devices are the pigments: Cyan, Magenta, Yellow and Black. Performing a color sep-
aration process is needed for convertation of color information from RGB to CMYK.
The autotypical synthesis is a basis of reproduction a color image in printing pro-
cess. However, the autotypical equations for four-color printing are written as a sys-
tem of three non-linear equations with four variables. Therefore, a solving approach is
mathematically incorrect. Nowadays, the traditional color separation technology is
based on the use of ICC profiles of printing system. The RGB → CMYK transfor-
mation is proceeded according to the table values of characterization data of LUT
(Look-Up Table). It is a principle of searching a value by a comparison, not via calcu-
lation method.
Problem. Classical technology does not solve the problem of uniquel convertation
of the digital original image into the color imprint. The aim of the work is to develop
new methods of the digital processing of images in preprint processes for the repro-
duction of tone and color range of digital original image in printing processes. In spite
of this, these methods are needed for providing the optimal value of printing inks in
color separation for gaining the stable and saving printing process.
2 New Image Separation Information Technology
A new oppositional color space ICaS was developed as a result of the study of non-
orthogonal color spaces [1]. It serves as a connecting link during color changes from
RGB to CMYK. The conversion from RGB to ICaS is described by a matrix based on
the discrete Hartley transform. Also, the authors developed a method for determining
the nonlinearity index of colored inks reproduction on the imprints. This nonlineari-
ty index has become the only parameter that takes into account the color reproduction
features in the given printing conditions [2] in the new color separation technology
[3]. The projection of the color gamut of the printing process on a chromatic CaS-
plane was modeled. As a result of the analysis of these projections, a new principle of
color separation of the image with two color inks and black one was formulated.
The general vector equation of autotypical synthesis is reduced to a system of non-
linear equations with three unknowns in accordance with the formulated principle:
I AU S K0 I ij + Si0 I j I ij + S 0j I i I ij + Si0 S 0j IW I i I j + I ij
C AU S K Cij + Si C j Cij + S j Ci Cij + Si S j CW Ci C j +Cij ,
0 0 0 0 0
(1)
S AU S K0 Sij + Si0 S j Sij + S 0j Si Sij + Si0 S 0j SW Si S j + Sij
where (I, C, S) – coordinates in space ICaS; subscript AU – denotes the color in auto-
typical synthesis; subscripts i, j, ij – indicate color of i-th, j-th inks and color that is
formed by mixing the i-th and j-th inks; subscript W – indicates the paper color; Si, Sj,
SK – relative dot areas of i-th and j-th inks and black (K) one.
The expression for the black ink is obtained from the achromatic coordinate IAU:
I AU
S K0 (2)
I ij I j I ij Si0 I i I ij S 0j IW I i I j I ij Si0 S 0j
A system of nonlinear equations for two color inks is derived:
00 10 Si0 01S 0j 11SM0 SY0 0
(3)
00 10 Si0 01S 0j 11SM0 SY0 0
The coefficients define determinants of the matrices 2×2 in this system of equations.
Expression for j-th ink has obtained from the first equation of system (3):
00 10 Si0
S 0j (4)
01 11 Si0
The quadratic equation (5), which has two solutions, one of which is valid, is obtained
as a result of substitution of expression (4) into the second equation of system (3):
a bSi0 c(Si0 )2 0 (5)
where a, b, c are specified by the values of the matrices determinants 3×3:
I AU I j I ij I i IW I AU Ii I ij
a C AU C j Cij Ci CW ; c C AU Ci Cij ;
S AU S j Sij Si SW S AU Si Sij
(6)
I AU I ij I i I j IW I AU I i I ij I j I ij
b C AU Cij Ci C j CW C AU Ci Cij C j Cij ;
S AU Sij Si S j SW S AU Si Sij S j Sij
The described analytical model of autotypical synthesis of colors on the imprint be-
came the basis for the new ICaS-ColorPrint information technology of image color
separation [3]. The authors developed a computer program ICaS-ColorSynthesis [4],
in which it is possible to prepare the image for printing using the new technology,
carry out a quantitative analysis of the consumption of inks.
3 Creating a Database of Non-Reproducible Colors
In the process of color separation, colors that can not be reproduced in the target color
space must be converted (gamut mapping). Traditional technology uses four basic
color rendering intents, which are recommended by the ICC specification.
For a certain set of colors of the original image we have obtained non-permissible
solutions of the autotypical synthesis equations: the negative values of relative dot
areas of printing inks, numbering more than 1, and complex numbers. This means that
such colors are beyond the color gamut of the printing process. We have been provid-
ed a color replacement for the first two cases taking into account two components of
color: the color tone and chromaticity, using the CaS-diagram.
If the solutions of the equations of autotypical synthesis are complex numbers (7)
the replacement of colors is not done correctly. Therefore, there was a task of tech-
nology improvement by creating a non-reproducible color database for this case.
Consider a more detailed analytical solution of the autotypical synthesis equation,
namely, its subroutine expression:
Si0
1
2a
b b 2 4ac , b 2 4ac 0, if b 2 4ac (7)
If the condition of formula (7) holds, the solutions of the equation are complex num-
bers. It was developed an algorithm for locating non-reproducible colors. It includes:
determining the coefficients b, a, c of equation (7), checking the condition and sorting
them by the achromatic coordinate (I) in the space ICaS. This method allows the color
replacement of the original and keeps in the maximum as possible degree of correct
and reliable transmission of tones and colors of the original.
Fig. 1. Presenting colors on CaS-diagram that cannot be reproduced within the CMYK
The Figure 1 shows the visualization the colors that cannot be reproduced by the
CMYK printing inks. These colors belong to two color gammas, formed by mixing
cyan and magenta inks, and magenta and yellow inks. These colors form planes which
were sorted by the level of achromatic.
The color database and the corresponding replacement is designed for two stand-
ardized print conditions: (Fogra51) and (Fogra52). The Relative Colorimetric color
replacement method has been used. In this method, the image colors are recalculated
relative to the white point of the output device. For the vast majority of cases, this
method shows its high efficiency. According to the described method, a database of
non-reproducible colors can be created for any printing conditions.
4 Comparison of Color Separation Technologies
ICaS-ColorPrint information technology for image separation is based on the princi-
ple which implies that every color of original image is created by only two color and
third one is black ink. The color position on the chromatic CaS-diagram determines
which two color inks are used in the synthesis. Consequently, this fact suggests that
the use of developed technology in the process of preparing images for printing will
provide savings of color inks. It is important that, in this approach, the visual identity
of the imprints obtained from a separation that uses a smaller amount of color inks
and with separation using the ICC-profiles is preserved. It is advisable to perform a
comparative analysis of the results of color separation using two technologies accord-
ing to the following indicators: the percentage of saving color inks and the value of
color differences between imprints.
There were held tests of printing a great set of color digital images. We used inkjet
printer for color proof to perform test printing, Spectrolino spectrophotometer for
colorimetric measurements, SpectroScan robot for precise positioning and automated
measurement and the ProfileMakerPro software package.
Here, to compare the results of color separation using two technologies, the
testchart was used as a test image, which consists of 192 control patches. The color
data of each patch of the testchart is converted from the RGB model to CMYK mode
by classical technology and by ICaS-ColorPrint technology. ICC-profile based on
characterization data Fogra51 was used for color separation in Adobe PhotoShop
software. With the new ICaS-ColorPrint technology for the same print conditions
(Fogra51) the calculation of autotypical equations has been applied using ICaS-
ColorSynthesis application.
It is possible to compare two technologies of color separation by quantitative indi-
cators in one software environment ICaS-ColorSynthesis 2.0 [4]. The program pro-
vides complete information on the average relative dot area of each ink for the whole
image, the value of the total relative dot area and TAC (total area of coverage) of
color and black inks. A quantitative analysis of color separation was implemented.
Saving color inks for the given test chart is 37%, and saving of all inks is 18%.
The international standard ISO 12647: 2013 estimates the accuracy of the repro-
duction by the color differences (ΔЕ) between the original and the imprint, or between
two imprints. Color difference is determined by the formula ΔЕ 1976. As part of our
study, the color differences between the corresponding patches of test image on two
compared imprints were determined. As an example, the relative dot areas of CMYK
inks are shown only for some of the patches in Table 1. The inks savings for each
patch of test chart were calculated, as well as the color differences between the corre-
sponding color patches of the two compared printed images. Average value of ΔE is
1,58 units, maximum 2,51 units. Such values are permissible and the difference be-
tween the color patches visually is not noticeable.
Table 1. The percentage of saving color inks and the value of color differences between two
imprints with using classical and ICaS-ColorPrint color separations
Name Color separa- Color separation Save inks Color differences
of tion with with ICaS- using ICaS- between two printed
patch ICC-profile ColorPrint ColorPrint images
C1M1Y1K1, % C2M2Y2K2, % Σ CMYK, % ΔЕ, unit
A1 37;65;57;60 0;47;43;77 24 2,16
A2 27;30;30;11 0;11;12;42 34 1,48
A3 50;31;69;46 25;0;57;69 23 1,24
A4 9;93;70;32 0;89;69;42 2 1,89
A5 87;25;55;50 84;0;52;64 8 2,46
A6 67;46;23;29 51;24;0;56 21 0,94
A7 35;35;63;39 0;7;46;65 31 1,99
A8 33;46;31;20 0;27;7;53 33 1,65
For the theoretical forecast of the saving inks, it has been numerically calculated the
autotypical synthesis equations for an arbitrary color. A number of possible correla-
tions of CMYK inks have been obtained. The resulting series of correlations has two
boundaries: the reproduction of the given color by the three CMY colored inks and
the two color and black one. The reliability of the calculations with great accuracy is
confirmed by experimental data. As a result of the experimental research, it can be
argued that the color separation of digital originals using autotype equations, basic
color vectors of inks and the index of non-linearity of the printing process enables to
save color inks and thus provide colorimetric accuracy of color reproduction.
5 Conclusion
In this paper new methods of the digital processing of images are presented. They
demonstrate a fundamentally new approach to the implementation of the process of
color separation and save inks with a significant extent.
Analytical solutions of the autotypical equations of the image synthesis on the im-
print with colored inks which have been obtained due to the using of a new color
space ICaS. This result allowed us to create a new analytical model of the color syn-
thesis on the imprint. Therefore, the computer program ICaS-Color Synthesis-2 was
developed. In this program was implemented the method of definition and replace-
ment of colors of original, which physically cannot be reproduced in printing, devel-
oped by the authors. A database of these colors was created for standardized print
conditions that can be expanded for particular production conditions.
New methods of the digital processing of images and their software implementa-
tion are the basis of the new information technology of color separation ICaS-
ColorPrint. New technology testing was completed and was compired with classic
one by quality and quantitative indicators. The obtained results confirm the economic
effect and quality of color reproduction.
References
1. Shovheniuk, M.V., Kryk, M.R.: An analytical solution of autotypical equations of image
synthesis in the color space ICaS. In: Reports of the National Academy of Sciences of
Ukraine, Iss. 11, pp. 81–86, (2012).
2. Shovheniuk, M.V., Zanko, N.V., Pysanchyn, N.S.: Characteristics of the prints of the triad
colors in the color space Adobe RGB. In: Computer technologies of printing: Technical
sciences, Lviv, Iss. 19, pp. 203–222, (2008).
3. Shovheniuk, M., Semenіv, M., Kovalskyi, B., Glushchenko, A., Nazarenko, V. (2019):
Method for separating the colours of a digital image into two coloured inks and black ink
for four or more colour printing. WO/2019/074467.
4. Kovalskyi, B.M., Semenіv, M. R.: Computer program of image synthesis for imprint for
new information and traditional technologies of color printing. In: Science and Education a
New Dimension. Natural and Technical Sciences, IV(10), Iss. 91, pp. 72–78, (2016).