IARIGAI Dubrovnik – Cavtat 2003, Croatia – Advances in printing science and technology: proceedings of the 30 th International iarigai Research Conference; UDK 655:004.91 > (063); 004.91:655 > (063); ISBN 953-96276-6-4 (tvrdi uvez); ISBN 953-96276-7-2 (meki uvez), Acta Graphica Publishers

New screening elements in multi-colour printing for special purposes

Jana Žiljak, Vesna Vančina, Darko Agić, Ivana Žiljak, Klaudio Pap

Faculty of Graphic Arts, University of Zagreb
P. O. Box 225, HR-10001 Zagreb, Croatia


This investigation determines new procedures of screening applied to multi-colour reproduction. Total individualisation of the image is obtained by introducing the new different screening system for each separation. This process is extended to the microstructure of the individual screening shapes, which was not described until now. Understanding of such procedures is closely linked to security printing, and therefore details are poor and not accessible. Solving of such problems involves team-work in various fields of research: design, prepress, materials in graphic processes, mathematical definition of screen systems and shapes, as well as protection methods for valuables. Proposed methods are performed by PostScript programming of output devices, optical measurements and experimental digital printing, using special, as well as conventional inks.

1. Introduction

The first presentation on specially designed screen patterns #1 (Iarigai 1999) with new applications of screen elements emphasized the topic of security printing and document application. Stohastic selection of screen patterns was suggested as well as stohastic attribution of lpi and angle for each pixel. The second article (#2) (Iarigai 2001) exposed four-colored application with individualized screening. It offered program-solutions as a combination of stohastic selection of screen parameters with a fixed screening element. While the first and the second report applied pixel graphic, and deconstructed image using a stohastic selection of lpi and a screen element type, this article discusses screening of vector graphics for printing with new screening patterns.

This article provides solutions for programming and application of new screening elements requested by digital printing techniques. It offers an original code for PostScript programming. Our applications fall under the area of complex integration of pixel and vector graphics: design for jumbo posters, documents and securities, as well as textile design. These applications do not involve only an image but also a structure of graphic interpretation creating the image. Portions of a graphic solution have been generated by PostScript algorithms.

2. Print

Surface objects of vector graphics are usually created as 100% spot colors. Designers emphasize use of spot colors hoping that each section of such a solution will result in print as a separate color. However, majority of their spot ideas result in four-colored CMYK screens.

Screening is necessary in case of designing of gradations and in majority of cases a standard AM or FM screening is applied. Since dotted image interpretation is considered as boring we have to minimize a screening element - "it is better when it is hidden". Tonal gradations in vector graphics should be screened and not printed with full tone. It would cause problems with color register and trapping. If a continued tone is dealt with a screen, a screening element should change its shape, whatever its size. It means that if a screen element is a crucifix it should be deformed in continuity depending on planned bolding within a defined microstructure. An example is presented of a continued transformation of a screen element propeller r14 as a print-out of liniature two screening elements per inch compared when the object is interpreted with continued changes (Figure 1), and when the object is bolded uniformly by 70% (Figure 2) and 15 % (Figure 3). Each example is associated with the original PostScript code (program 1, 2, and 3).

/r14 {dup 2 index 3 exp sub abs sqrt 3 1 roll 3 exp add abs sqrt exch sub abs 1 exch sub} bind def

Figure 1 Propeller R14
L K {r14}bind setscreen 0 1 250 div 1 {/g exch def g setgray 0 0 moveto
160 0 rlineto stroke 0 -0.8 translate }bind for

Figure 2
1 45 {r14} bind setscreen 0.3 setgray 0 0 moveto 150 0 rlineto 0 -150 rlineto -150 0 rlineto closepath fill

Figure 3
1 45 {r14} bind setscreen 0.85 setgray 0 0 moveto 150 0 rlineto 0 -150 rlineto -150 0 rlineto closepath fill

In cases where a solution calls for lines only (special interest lies with protective lines for documents), at present practice reaches for drawing and copying using vector graphics. Such a protection is not adequate since these programs are readily available. This article suggests a solution for line graphics by screening along an object placed under it. In case of selecting a screening element with a pattern of a twisting line, it is recommended to program a base as a continued full gradient shading. It is necessary to have an algorithm for designing that screening element. Screening the segment of an image with a low lpi will result in line base that cannot be interpreted with programs for vector graphics.

The next step in application is the use of two or more colors with various patterns of screening elements. Each color requests a separate procedure. Low lineatures will create a special impression. Such a three-colored solution has been applied to the Croatian currency Kuna and improved this year with a new edition. One color reacts under ultraviolet light and another is visible in the infra-red range of the spectrum. At present we are planning solutions for each specialized application with a spot vector screening but the screening will be used only once.

This article presents seven unpublished images of screening elements and the reader may modify shapes of screening elements using the original code. These screening elements may be also used in vector and pixel graphic for printing. They can also be used for graphic solutions resulting from the PostScript program itself as presented on our Web pages #3 .

3. Programmable graphics

Microstructure of specialized graphic solution can be also created with copying tiny vector elements of an image. Such an file is huge so the question is whether we have a computer that can follow up within a reasonable timeframe how a designer develops an idea. On the other hand, programmed shape of a screening element does not burden computer’s memory and speed. The screening is carried out through an act of display or a print-out. Shapes of these tiny elements are not stored in the memory. There are no Bezier points that overflow the vector graphics. There is only an algorithm on the manner of processing, showing how a drawing has been created for a display i.e. for printing. Preference is for programmable graphics that has not been recorded as vectors or pixels. In the same document a designer may use numerous screening elements, planned or visualized on the monitor or a printer. Programmable graphics may create both pixel and vector graphics. As noted earlier programmable graphics has been generated during display. This article contains PostScript algorithms with maximum reduction, simplified for screening vector graphics with new screening elements. Deliberately we have created a very clean algorithm without a PostScript indirect adressing in order to encourage further research by other graphic artists especially younger ones. More detailed contemplation of the algorithm structure should lead to the creation of a large library of screen patterns and enrich a tendency towards personalization in the printing industry.

Programmable graphics is generated graphics, generated design, created by algorithms, mathematical procedures and parameter tricks. Although this article does not cross into the area of fractals let us mention that programmable fractals present the most interesting area of developing personal approach to design and digital press. The application of fractal principles will enrich the microstructure of a screening cell. It will result in new proposals for development of FM screening especially in the application of printing with ten different colors.

4. Experimental tests

A three-dimensional, two-dimensional pattern and an active screen may be depicted and named freely. All proposed screens have been shown as bolded continually (zero to 1, loop from 0 to 250, step 0.004). Example (b) shows an application with the same screen or in a combination with another one. Screen names are: /r2, /r3, /r4, /r5, /r12, /r14 and /r16.

/r2 Dropping Eiffel: filling a screen up changes a shape from the imitation of a letter Y,a drop, houses and roofs.
/r3 Cut Glass: a crucifix linked to a dot shades into a closed window
/r4 Wheat Ear : a light linear structure is complemented by an ear, it shades into six horns
/r5 Hanger: columns with a triangle suspended to
a horn-shaped column
/r12 Coffee: linked dots progress towards a coffee bean
and a cat’s eye
/r14 Propeller: propeller-shaped dots ranging from light to dark shade over from a white to a black propeller
/r16 Bat: a dotted ornament shades into a crown and a bat

/r2 {dup mul exch 3 exp 2.71828 exch exp exch sub 2 div abs 1 exch sub} bind def

/r3 {dup 2 index dup dup mul mul mul abs sqrt 3 1 roll dup dup mul mul mul abs sqrt exch sub
abs 1 exch sub} bind def

/r2 Dropping Eiffel
/r3 Cut Glass

gsave 0.6 setgray 100 300 translate 0 0 moveto 300 0 rlineto 0 200 rlineto -300 0 rlineto closepath 15 45 {r2} bind setscreen fill grestore gsave 160 450 translate /FSHelvetica findfont 60 scalefont setfont /g 0.2 def 8 {0 0 moveto (IARIGAI) false charpath g setgray 15 45 {r3} bind setscreen fill /g g 0.09 add def -8 -20 translate} repeat grestore showpage

/r4 {dup 2 index dup 2 index exch div floor mul sub 3 1 roll dup 2 index exch div floor mul
sub sub 2 div abs 1 exch sub} bind def

/r5 {exch dup mul dup 2 index dup 2 index exch div floor mul sub 2 mul 3 1 roll dup 2 index
exch div floor mul sub exch sub 3 div abs 1 exch sub} bind def

/r4 Wheat Ear
/r5 Hanger

/polje [{r4} {r5} ] def /L 7 def %linijatura /K 45 def %kut /polumjer 50 def /siva 0.9 def gsave 250 300 translate /j 0 def 7 { siva 0.1 sub /siva exch def siva setgray 0 0 moveto 0 0 polumjer 0 360 7 div arc 0 0 lineto 50 10 add /polumjer exch def closepath 7 45 polje j get bind setscreen fill 360 7 div rotate /j j 1 add def j 1 gt {/j 0 def} if } repeat grestore showpage

/r12 {dup 2 index 3 exp sub abs sqrt 3 1 roll 3 exp sub abs sqrt exch sub abs 1 exch sub} def

/r12 Coffee
gsave 0.5 setgray 100 300 translate 0 0 moveto 300 0 rlineto 0 100 rlineto -300 0 rlineto closepath L1 K1 {r12} bind setscreen fill grestore gsave 100 310 translate /FSHelvetica findfont 50 scalefont setfont 0 0 moveto (DUBROVNIK) false charpath 0.4 setgray L2 K2 {r14} bind setscreen fill /FSHelvetica findfont 40 scalefont setfont 0 50 moveto (IARIGAI) false charpath 0.4 setgray L2 K2 {r14} bind setscreen fill grestore

/r16 {dup 2 index 3 exp abs sub abs sqrt 3 1 roll 3 exp abs add abs sqrt exch sub abs 1 exch sub} bind def

/r16 Bat
/L1 12 def /K1 45 def /L2 8 def /K2 45 def /sp 100 def /vp 500 def /brojsiveskale 250 def /dlinije vp brojsiveskale div def dlinije setlinewidth /j 0 def gsave 0.5 setgray 100 300 translate 0 0 moveto 300 0 rlineto 0 100 rlineto -300 0 rlineto closepath L1 K1 {r12} bind setscreen fill

100 310 translate
/FSHelvetica findfont 50 scalefont setfont
0 0 moveto (DUBROVNIK) false charpath

0.4 setgray L2 K2 {r14}
bind setscreen fill
/FSHelvetica findfont 40 scalefont setfont
0 50 moveto (IARIGAI) false charpath
0.4 setgray L2 K2 {r14} bind setscreen fill

5. Design and personalization

Designers still do not realize that even internal screening structure calls for special even perso-nalized solutions. The use of low liniatures of good visibility could bring sophistication into design. A question is how to create interesting screen structures that are not usually found around us. This article encourages designers to use new ideas in screening their graphic designs.
Personalization has rocked the application of graphics, first in relation to security printing of documents and later through its application. Since personalization has proved its efficient application, it led to application at-large and abundant ideas. Personalization has been carried out everywhere, at all times and using all technologies. Our focus lies with the personalization in screening elements. The initial data or a seed for generating an incidental series of numbers that are selected for a screening element may be taken from a data with a personal value e.g. a date of birth or a car license plate. Such thinking will lead us to personalized printing at a level of a screening cell and a solution could be repeated only when possessing both pieces of data: the initial number and the algorithm used for screening.

6. Conclusion

At present a printing product results from a team effort, specialization and quick adaptation to advanced technologies. In the imminent future, designers’ projects will become more complex, have more contents thus demanding original solutions that use new materials and colors and diverse technological procedures. Optimal approach to productivity will be embraced by printing companies and designers prone to flexibility and adaptation to possibilities available to the printing industry at a certain environment. A graphic solution may be elaborated in various manners with minor differences. It is necessary to study all new proposals resulting from digitalization and Internet, to review them and build them into procedures for creating a graphic product. Screening an image, a graphic pattern and colored surface is a special trait of the printing industry. Methodology for display and visual presentation of a screening solution varies for each technology and it is completely different for Web, print, video and other aspects of multimedia. This article discusses new screening elements for print only that refer to personalization, digital printing, original visual solutions and their special application in designing documents. For these areas we have used printing with original screening elements thus opening up new opportunities with the creation of databases of new screenining elements and novel application in printing. This development is aimed towards a stohastic definition of screening types. The article offers original PostScript solutions with a sole purpose of creating interest with graphic artists and designers and providing incentives for their application in solutions for graphic products. We have tried to study the most detailed interpretation of screening printing and clarify all doubts so that the screening methodology could be used efficiently in a novel manner in the printing industry.