quarta-feira, 9 de setembro de 2009

TETRASTICH SCREENING PROCESS & STEREOFLEXOGRAPHY

- O hardware STEREOFLEXOGRAPHY (resumo e fotos do protótipo, abaixo),, desenvolvido, para, uma nova, geração, de equipamentos flexográficos de pré-impressão, que originou a plataforma de software TETRASTICH, possuem seus respectivos pedidos de patentes depositados no PCT e USPTO, e publicados nos links:
- Reportagem completa sobre o PROCESSO DE RETICULAGEM TETRÁSTICO publicada pela revista PrintCom World (português/BR) nas páginas escaneadas, abaixo, ou no link:
http://www.printcomworld.com/data/fulltextarchive/pdf/pb0021/PB_2005_04_86.pdf 





TETRASTICH SCREENING PROCESS

THE PARADOXICAL SCREENING SYSTEM AM+FM FOR CMYK PRINTING WITH SQUARE DOTS OF THE SAME SIZE RANDOMLY ORGANIZED.
The Tetrastich Screening Process* is a new platform that is going to enable the solution of the main problems existing in the old Rosette Pattern with dots aligned in angles of varied sizes with AM (Amplitude Modulated), and in the Stochastic, with dots placed randomly of the same size, FM (Frequency Modulated), both, in their respective screenings of four subtractive colors CMYK (Ciano, Magenta, Yellow and Black).
In 1982 Gerhard Fischer, already in the digital era, patented the first algorithm to produce screenings with dots of the same size randomly distributed (FM), with the objective of solving the problems caused by the Rosette and Moiré effects, seen in the polychromatic reproductions of halftone, aggravated by incorrect angles of the screenings and/or deficiency in the inks. One of the palliative to solve these problems was the development of AM/FM Screening that mixes both processes in a complementary form, without adding substantial advantages or eliminating the deficiencies seen in both.
Nowadays, the laser spots generated in the Computer to Film (CtF) and in the Computer to Plate (CtP), assume all the imaginable dots forms, with varied sizes or of the same size, in angles or randomly, placed without greater operational problems in their respective CMYK screenings. However, the difficulty in diagnosing their main problems does not allow to compare and to identify which one of these intricate screenings offers the best quality of impression.
Fig. 1 – Several screenings in the Rosette Pattern with CMYK register and dots Amplitude Modulated (AM).
In the enlarged illustrations (Fig. 1), we see some examples in the Rosette Pattern using screening of angles with several dot formats, all with the same percentages and lines, printing the spots: Round, Square, Diamond, Elliptical, Euclidian, Inverted Round, Inverted Square and Spot Line, aligned in angles and with CMYK registers, where the yellow color was suppressed because it would be practically invisible due to the Rosette Effect, that impinges the overlap of the other colors before eliminating all the white base of the substratum, generally paper.
We observe that the impression of any dot format with variable size aligned in angle in their screenings, even when printed in high percentiles, does not suppress completely the substratum base that simulates a fifth parasite color, complicating very much the forecasting of the results and complicating the obtaining of a better color definition and quality of impression, besides generating imperfections and undesirable stains which demand solutions that increase very much the costs of the printing process.
The square dot is the only one that has conditions of integrally covering an area not needing overlap imposed when we use other dot formats. But this quality is lost when we superimpose this same format in angle screening, which introduce amongst others problems the increase in ink consumption and the unpredictable polychromatic interactions of difficult diagnosis, demanding the development of sophisticated programs of color management and calibration of monitors.

Fig. 2 – Processes Rational Tangential and Irrational Tangential.
In the enlarged examples (Fig. 2) with details in gray to facilitate comprehension, we see two attempts of putting dots of the same size (FM), in a non random way, aligned in screenings of angles CMYK. The Rational Tangential Process disposes the square dots in complicated geometrical screenings which are only possible, in the 45°, 90°, or 0° angles; while the Irrational Tangential Process uses algorithms that calculate several alignment angles assuming negligible errors in the placement of these dots in their respective screenings. Due to heavy and complex calculations, which require big processing capacity, the cost benefit relation complicates the commercial acceptance of these processes by the graphic market.
The Tetrastich Screening Process has as characteristic, to seize the advantage of the versatility of the square dot of the same size, similar to the FM, organizing these dots side by side, with zero angle, without overlapping them, and to vary, similar to AM, the size of these dots as function of the percentiles necessary for the halftones dispensing, with this, the need to align them in angles and to place the four colors, separately, in each one of the four vertexes or sides of their respective cells of the CMYK register. Therefore, with these characteristics we can conclude that the Tetrastich Screening are the processes AM and FM, added up.

Fig. 3 – Tetrastich Screening with CMYK cells varying from 1% ~ 99%.

With the Tetrastich Screening disposing, side by side, square dots of the same size, even in any percentiles of halftones, we reduce the remaining white substratum at a superior rate to the other processes, besides facilitating the most adequate choice of which vertex or side we are going to oppose or join two colors that interplay negatively or positively.
In the enlarged illustration (Fig. 3) we see one of the several forms of disposing the square dots of the same size according to the Tetrastich Process, with percentiles varying in intervals of 1% to 99%, with lines in gray and in the CMYK colors to facilitate the visualization and comprehension. The symmetrical disposition regarding the diagonal of the cell offers the best results compared to an asymmetric disposition, therefore in the later examples we are going to analyze, only, the symmetrical disposition.
As we can observe in the enlarged illustrations (Fig. 4), we see a same Tetrastich Cell disposed at zero angle, to the left, and at 45°, to the right, with Ciano 22%, Magenta 20% and Yellow 25%, diagonally, with Black 19%, with coincident CMYK registers varying from 1% ~ 99%. It is opportune to explain that Tetrastich Screening with cells having 100 halftones (10 x 10) will demand 1200 DPI (10 x 120) for lines of 120 LPI, and with 256 halftones (16 x 16) will demand 3200 DPI (16 x 200) for lines of 200 LPI.
We see that the white remaining part was almost extinguished and the yellow continues, perfectly visible, even in low and average percentiles, without dots overlap, permitting combinations of colors with greater clearness and definition and, consequently, dispensing the need to do exclusive additional plates for the more problematic secondary colors.

Fig. 4 – Tetrastich Cells with CMYK register, to the left at 0°, to the right at 45°, both, with Ciano 22%, Magenta 20%, Yellow 25% and Black 19%.
This is an attempt of digitalizing the CMYK subtractive color system, to become compatible with the additive RGB color system, now both using the pixel, the smaller graphic unit of an image, and with this becoming faithfully compatible the color management programs with the calibration of the monitors, obtaining in polychromic impression exactly what one sees in video (WYSIWYG).
With the Tetrastich Screening we can develop, specially for the flexography area, a new anilox cylinder with its square micro-cavities of size and texture angle exactly equal to the one existing in the screening dots of the impression plate, and with this avoiding the dot gain increase by supplying the exact quantity of ink, since now there is the possibility of synchronizing, precisely, these micro-cavities with the dots of the impression plate.
With the organization of these cells, side by side, the Rosette Effect will be totally eliminated, and with the purpose of soothing the Moiré Effect we can dispose these cells from diagonal to vertical of the substratum in an angle of 45°, as we observe in the enlargement (Fig. 5), profiting from the limited human eye acuity for the oblique structures.


Fig. 5 – The Tetrastich Screening Process of cells with CMYK registers at 45°.
Having done the previous steps, we shall use an advanced codification algorithm to randomly rotate all the cells at 0°, 90°, 180° or 270°, as we observe in the enlargement (Fig. 6), breaking the optic interference standard originated by the proximity of two or more geometric and regular periodic sequences and thus completely eliminating the Moiré Effect.
We observe that a CtP established with a fast optic semiconductor (DMD), which modulates more than 1 M dots (pixels) at the same time, digitalized in a fixed matrix of micro-mirrors with low contrast resolution, has as limitation the fact of operating only with Stochastic Screening (FM), its only advantage if compared tour only disadvantage compare to CtP with laser that module dots with several spots percentile and formats, could operate with the process AM and or FM. With the dots organized without overlap provided by Tetrastich Screening, this disadvantage will be eliminated allowing that a ´Computer to Plate´ made with DMD shall add this larger speed with printing quality, besides the ink big saving. In the future, these qualities will be extended to a ´Computer to Press` with DMD, that will be the best option to save toner, solid or liquid, in digital printing or in the continuous processing equipment that will dispense impression plates in the offset and flexography sectors.
Without any paradox Tetrastich Screening is a revolutionary process, which is at the same time random and organized, associating the systems AM and FM in a simple and functional way, without side effects that might harm the possible advantages provided.



Fig. 6 – The Tetrastich Screening Process AM+FM of cells with CMYK registers.
This is a highly polemic subject and of difficult consensus, so it would be of great pretense to imagine that this first presentation of the Tetrastich Screening Process* would be enough to satisfy the conservative and the innovative, before become necessary the due improvements impinged by the practical establishment of the Tetrastich Software.
Brazil, Rio de Janeiro, 2002 ~ 2006.


.* Patents Deposited


STEREOFLEXOGRAPHY

ABSTRACT

Improvement to the photopolymers catalysis in printing plates for the flexographic and of stamp sectors, by exposing the photopolymer plate, only, by the bottom face, to two different and simultaneous levels of radiation; a lower, to catalyze the base of the relief and a maximum, to catalyze the printing relief, emitted by radiation device, polarized by filter, which uses a negative film whose black area is replaced by halftone, thereby originating the low radiation level, and keeping its transparent area, thereby originating the maximum radiation level, thickening the base of the dot and sharpening the top of the dot, thereby eliminating the 'dot droop' and the 'dot gain’, respectively; or which uses optic semiconductors, which digitally modulate the radiation in a fixed way for the stamp sector, with DMD or LCD.

Below, the first 3D printer prototype developed in Brazil, in 2001
(Abaixo, protótipo da primeira impressora 3D desenvolvida no Brasil, em 2001)








1), and in a mobile way (fig.3), with DMD (1), for the flexographic sector.

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