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You are here: Conferences & Events * 2011 Budapest * Abstracts * 4. Color Processing

4. Color Processing

4.01 Evaluating color-difference formulas in LCD-based soft-proofing

Maria Fedutina, Philipp Urban, Edgar Dörsam

The prediction performance of three color-difference formulas (CIE76 - Euclidean distance in CIELAB, CIE94 and CIEDE2000) was evaluated on an LCD (Liquid Cristal Display) typically used in soft-proofing applications. For this purpose we conducted an LCD-based visual experiment to analyze perceived color differences around five color centers recommended by the CIE and created a new color-difference dataset. The performance of the color difference formulas to predict these perceived differences was evaluated by the STRESS index, which allows also a statistical analysis whether one formula is significantly better than another. It was found that the CIE94 and CIEDE2000 formulas perform significantly better than CIE76. For default parametric variables (kL= kC = kH =1) the CIEDE2000 formula performs significantly better than the CIE94 formula. If the parametric variables are optimized both formulas perform almost equally. We analyzed the over- and under-fitting behavior of the formulas and could verify the results of other investigations that predicted color differences on typical LCDs are perceived smaller than similar differences on hard-copies.

Keywords: STRESS; color difference; F-test; LCD
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4.02 Colour effect changes at security graphics due to print media and colour sequence

Erzsébet Novotny, Rozália Szentgyörgyvölgyi, Pál Görgényi-Tóth

At colour reproduction of security graphics, there are often significant colour distortions resulting from the features of design, approval and production processes associated with guilloche patterns. The overall colour effect of the printed product may differ from the approved graphic design or proof as well. The colour effect differences are due to a number of reasons: printing technology, different colorimetric properties of inks and base materials, etc. Changes to the sequence of colours being printed may also lead to deviations in colour.

We realised that most of researches are concerned with the colour management problems of four-colour printing, while the direct-colour line art reproduction has received much less coverage. Because of it our research aimed to determine the extent of colour distortions generated during the security graphics reproduction and identify the reasons for variations in colour effect.

We examined the changes in line thickness and colour of the patterns. We concluded that, in order to get the proper colour effect, the printing order of colours and the vertical or horizontal position of security graphic elements on the sheet must definitely be specified during the design process.

Keywords: security printing, guilloche design, line art reproduction, colour measurement
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4.03 Characteristic analysis of the primary color inks in color print

Mahziar Namedanian, Sasan Gooran

Characterization of color inks gives proper insight to the behavior study of inks such as penetration and spread on paper. By sending a light with a wavelength in the reflective wavelength interval of a color ink, the ink becomes totally transparent, and therefore disappears from the paper. In color prints, due to the fact that the color inks are not ideal, it is hard to find a wavelength band at which one color ink completely absorbs the light and the others completely transmit it. In this situation, the color inks, which transmit the light, cannot be thoroughly removed from the paper and their shadow remains. In this paper, in order to separate the shadow, we propose a simple approach based on the reflectance histogram of microscale images captured by a high-resolution camera. By separating the effective dot area of different color inks, it is possible to study the ink behavior once when it is printed individually on the paper and another time when it is printed with other color inks. The result of this study provides useful information to paper and ink manufacturers, and also the graphic art industry.

Keywords: microscale image, reflectance histogram, dot gain, color print
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