彩色印刷正比特性与叠加特性缺失问题探讨

彩色印刷复制系统的色域范围受多种因素影响和限制,正比特性缺失及叠加特性缺失就是其中两个重要因素.正比特性缺失是指网目图像的反射特性与其对应的实地墨层的反射特性不成比例的状况;叠加特性缺失是指两色或多色叠印的密度与相应单色的密度之和不相等的现象.造成两种缺失的原因有印刷系统承印物/油墨组合的光学因素和物理因素,如承印物表面的反射、印刷区域多次的内部反射、网点的结构、油墨的非正常吸收特性以及墨层叠印不良等.这两种缺失特性问题可通过选择正确的复制工艺、承印物及采用适当的加网,或者通过补色或专色油墨、亮光油的印刷以及改变色序等措施来克服.

Analysis of the Proportionality Failure and Additivity Failure of Color Printing Systems

The gamut of a color printing system can be affected or reduced by many factors. The proportionality failure and additivity failure of the color printing system are two of them. Proportionality failure occurs when halftone tints of a given solid ink film fail to retain their proportional reflectances. Additivity failure occurs when the densities of a two-color overprint fail to equal the sum of the densities of the two primary-color inks used to produce the overprint. The causes of these failures include the optical and physical factors of the substrate/ink combination, such as paper surface reflections, multiple internal reflections, the halftone dot structure, the unwanted absorptions of the inks, and undesired trapping between two adjacent ink films, etc. Both problems can be countered by the right choices of the printing processes, substrates and the halftone dot structures, or by the measures of using supplementary inks or inks of special colors, overprint varnishes or coatings and changing the color trapping sequence, etc.