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Proceedings Paper

Effects Of Unsharp Masking On Color Reproduction
Author(s): R. K. Molla
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Paper Abstract

Unsharp Masking, abbreviated as USM, is one of the few terms that is transferred from photographic color separation technique to modern electronic separation in a scanner. In photographic separation, the color correction mask is made unsharp to enhance details in the reproduction. In a color separation scanner, the principles remained the same, however, a different technique is used to create an optical illusion to enhance sharpness or details in the reproduction. During scanning, when there is a change of density in the copy, two fine lines are generated at the borders of the transition, a lighter line and a darker line at the borders of light and dark edges respectively of the density change. This is possible by scanning the copy with the main aperture as well as a separate larger aperture called unsharp masking aperture. When the separation is in progress, the signal from the unsharp masking aperture is compared with the signal from the main scanning aperture at a differential stage in the computer. If there is a density change in the copy, the larger unsharp masking aperture senses the change sooner than the smaller main aperture, and at this point, an additional signal is generated and added to the main signal. This makes it possible to create the black and white lines at the borders of a density change. In addition to this function, the same black and white lines can also be produced at the borders of transition of a color by transmitting the unsharp masking beam through any one of red, green, or blue filters. A combination of these apertures and filters can be selected by adjusting a pair of wheels located on the scanning head as in Hell scanners, or by changing specific inserts as in Dainippon Screen scanners. When used moderately, the black and white lines at the borders of a density or color change will create the effects of sharper details in the reproduction. In addition to the above mechanical controls, electronic controls are also provided in most scanners to increase or decrease details and, if necessary, to suppress any unwanted enhancement in certain areas of the reproduction. The presentation explores the various types of detail enhancement and suppression controls used in a scanner and their effects on the reproduction.

Paper Details

Date Published: 12 June 1990
PDF: 12 pages
Proc. SPIE 1184, Neugebauer Memorial Seminar on Color Reproduction, (12 June 1990); doi: 10.1117/12.963906
Show Author Affiliations
R. K. Molla, West Virginia Institute of Technology (United States)

Published in SPIE Proceedings Vol. 1184:
Neugebauer Memorial Seminar on Color Reproduction
Kazuo Sayanagi, Editor(s)

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