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UCA , under color addition ajout de sous-couleurs Process within achromatic composition to compensate for its deficits in brilliance and contrast; in this process, small quantities of the under colors CMY, which had previously been reduced to zero, are increased again in the “under colors” (neutral image depths and three-quarter tones), leading to an improvement in black. This also leads to a smooth transition to the chromatic color separation with UCR.

UCL , Universal Color Language langage universel des couleurs basis for understanding introduced in 1965 by K.L. Kelly and improved in 1976 concerning color names, compiled in a dictionary; with terms, among others, like bright, pale, strong.

UCR , under color removal ajout de sous-couleurs modified chromatic composition in which the CMY components (tertiary colors) jointly involved in the shadow areas of the image (threequarter to full tones) are replaced by a “short black”. The purpose is the reduction of the total ink coverage to significantly less than 400% to prevent drying and wet-on-wet ink trapping problems. When this reduction is extended to all areas of the three-color gray, this is gray component replacement (GCR) with a “long black”. There is no clear-cut transition to GCR: slight, medium and strong UCR with the maximum GCR, characterized by the increasing “length” of the definition black, going as far as the possible elimination of one of the process colors if it only makes a contribution near the gray axis. Today, optimum UCR and GCR settings are also anchored in highquality ICC printing condition profiles and DeviceLink profiles like those made freely available by basICColor, for example, at www.colormanagement.org.

UCS , Uniform Chromaticity Scale see CIELUV

Ulbricht sphere spectrophotometer spectrophotomètre à sphère device whose purely diffuse measuring geometry (di:8° or di:0°) makes it possible to measure colors on high-gloss and curved surfaces as well as surfaces with metal and interference effect pigments, where devices with 45°:0° geometry fail. Color measurement results obtained using different measuring geometries are not comparable.

under-color addition ajout de sous-couleurs see UCA

under-color removal see UCR

UV curing séchage sous UV application of the short-wave invisible range of optical radiation for drying printing inks, inkjet inks and varnishes (hardening of the layers); UV-C (280 to 100 nm) starts the radically or cationically induced crosslinking reaction by splitting up the photoinitiators, UV-B (315 to 280 nm) maintains the radical polymerization, UV-A (380 to 315 nm) penetrates thick layers. UV inks are preferably printed on smooth, non-absorbing surfaces (plastics, metalized substrates) and are available for all printing processes, espetransmitted cially in the printing of packaging (folding boxes, foils), labels (self-adhesive, in-mold labels), plastic cards and so on.

UV-cut filtre anti-UV filter in colorimetric measuring instruments which filters out the UV component from the irradiated light to be measured; application: comparison to measurements with UV component for the purpose of evaluating the optical brighteners in papers and printing inks.

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