Katharina Kehren, Edgar Dörsam, Heike Hupp

Abstract
Strategies for process control and quality assurance are well-established in printing with absorption inks. In the case of interference effect colours, usual optical parameters and common measuring geometries are not appropriate. A new optical parameter for process control and two necessary but sufficient measuring geometries for quality assurance were found.

Special properties of printed interference effect inks are outlined compared to conventional printing inks with absorption pigments. The comparison accounts for the necessity of adjusted concepts for process control and quality assurance. First examinations showed that the appearance of printed interference effect colours in fact depends on the thickness of the ink layer.

For interference effect colours, the difference between the lightness of the unprinted paper and of the printed result linearly correlates with the ink layer thickness. Therefore, the lightness difference is a suitable parameter to control the printing process by means of the ink supply.

Analyzing colour distances, two measuring geometries were found to be necessary but sufficient to represent aspect line and interference line in the a*b*-plane of the CIELAB-color space. Measurements of colour coordinates in the common geometry 45°/0°(+45°) far from gloss and the additional geometry 45°/-30°(+15°) near gloss guarantee the quality in printing.

Keywords: Interference effect colours, Process control, Quality assurance, Lightness difference, Measuring geometry
Contact: This e-mail address is being protected from spambots. You need JavaScript enabled to view it

Daniel Nyström, Li Yang

Abstract
Accurate determination of physical dot gain is essential for correct tone reproduction and for quantitatively evaluating the effect of optical dot gain. Due to the fact that, in reflectance measurements, physical and optical dot gains always co-exist, it is a difficult task to separate one type of dot gain from another. In this study we investigate three different methods to determine the physical dot gain, using spectral reflectance measurements, transmission scans and microscopic images of halftone prints. The different methods produce similar results and the good correspondence to experimental data confirms the validity of the methods. Further, the relation between the physical dot gain and the halftone dot size is investigated, by using FM halftones of various print resolutions. The physical dot gain demonstrates a clear correlation with the halftone dot size, with the increase in dot gain proportional to the increase in halftone resolution. The experimental observations are illustrated by theoretical analysis, showing that the physical dot gain is proportional to the nominal dot area, the side-length extension of the halftone dots, and the print resolution.

Keywords: Physical dot gain, Optical dot gain, Yule-Nielsen effect, Halftone printing, Print resolution.
Contact: This e-mail address is being protected from spambots. You need JavaScript enabled to view it , This e-mail address is being protected from spambots. You need JavaScript enabled to view it

Andrey Schadenko, Yuri Kuznetsov

Abstract
Fine detail distortion by the halftone dots is investigated with taking into account the quantization errors accompanying the image tone measure spatial dispersion in screening process. The number of these errors correction methods is discussed with illustration of models of test images reproduction.

Keywords: Halftone, screening, Quantization, Sampling, Error
Contact: This e-mail address is being protected from spambots. You need JavaScript enabled to view it