Concentric Screening And Its Replication Features

Dot is the most basic cell in printing, it takes on the task of organising the gradation,figure and the colour of the images, so the characteristic of the dot may directly affect the quality of the images which are reproducted. Optimizing the screening technology can get the presswork which have higher quaulity,and advance the value of the reproduction.Printing screening technology has had the history of 100 years, it goes through from handmade screening, photography screening, zoom electronic screening to digital screening in nowadays. Digital screening technology evolves from simulation screening technology, it develops gradually along with the development and the extending of computer hardware and software technology, peripheral equipment, image processing display technology and hard copy equipment since 1970s, it is the necessary demand of achieving digital pre-press. For years, digital screening arithmetic constantly brings forth the new through the old, it appears in turn Amplitude Modulated Screening, Frequency Modulated Screening, and mixed screening which include Amplitude Modulated Screening and Frequency Modulated Screening.Amplitude Modulated Screening is the most typical and frequently-used screening technology in pre-press. The space between the amplitude modulated dot can not change, while the size of the dot can change, and the dot shape are dot types which are designed, and it represents the image tone by changing the dot areas.The dots which have different shapes may have different change rules and different transfer characteristics of plate making and press in the process of the image reproduction, it will also bring the different reproduction effect.The AM screening usually use the solid dot, its shapes are mostly:square,diamondoid(rhombus,rotundity,ellipse,double dots and especial shapes.This paper try to realize a new dot shape of AM screening, namely:concentric screening. Aiming at the concentric screening, we try to realize this screening and acquire its reproduction characteristic by testing, then educe the optimum parameter of the concentric screening to expect that this technology can be applied well, and advance the quality and the efficiency of the reproduction, and at the same time, offer some gists for the optimized design of the dot shape.The method which is adopted:using the dot function of PostScript language to describe the shape of the concentric dot, by RIP disposal during the pre-press and the craft of the CTP plate making, the mechanical proofing, and then measure the plates and the printing samples, afterward measure the printing effect of the chromatic samples with your eyes, and finally obtain the printing reproductive transfer characteristic of the different shapes of the dots.The main processes of the experiment are as follow:after making the testing, we produce its PostScript file, then insert the concentric screening function which is compiled by ourselves or the Euclidean screening function into the file, after Ripping, we get the TIFF file, then we combine the TIFF files which have different dot shapes to a big version, then Ripping and outputting the plate by CTP, after that, we get the four-color plates, measuring the percentage of the dot area on the plates by plate testing instrument. We get the four-color proofs by machine proofing, then measuring the percentage of the dot area on the proofs by X-rite 500 spectroeye. Making the printing profile by the software of ProfileMaker, then we can get the results.According to the results, we analyse the printing reproduction transfer characteristic of Euclidean dot, Esko concentric dot and the user-defined concentric dot, then observe the four-color images of the proofs by eyes, and getting the subjective printing effect by eye survey.By the method of academic analysis and the experimental confirmation, we analyse and study the tone gradation transfer of the different shapes of the dots, compare the difference in reproduction characteristic between the ordinary Euclidean dot,Esko concentric dot and the user-defined concentric dot.