Abstract

Digital halftones as output on plain paper are the focus of this study. A new terminology is suggested to allow proper description of digital halftones. The most important of these terms is the use of "addressability" to replace the often misused term "resolution." Also important is the use of the term "spot" rather than "dot" to describe addressability. A means of properly describing digital halftones is suggested to avoid confusion with analog (ie., conventional photographic) halftones. Halftone patterns were created to test the efficiency of different designs at 300 spot per inch addressability on a laser printer. The page description language PostScript was used to create the halftone patterns which were modeled on three basic designs. It has been established that two halftone dot patterns constructed on the same matrix and containing the same number of spots will produce different densities if the configuration of the spots within the matrix is different This has been tested by comparing the results of the tone production curves of the condensed and open halftone dot designs. These patterns were output on a laser printer and measured for density. Tone production curves were drawn and compared. Even though each matrix contains the same number of spots, it has been shown that different densities result. This is solely a consequence of the dot design. Microscopic studies were conducted to illustrate the nature of the filling-in in the non-image area. Microscopic measurements were also made to ascertain the size of an individual spot at various screen rulings. It was found that the spot, which was very irregular to begin with, actually began to break up as the linescreen approached 150 lines per inch. Paper tests were run to gauge the maximum density and the tone production capabilities of various papers. Although the results were inconclusive, they point out another flaw of digital halftones which are output on plain paper. The number of grays predictable, given a matrix size, is greater than what is achievable in practice. These results mean the following for designers of digital halftones. First, purely due to the nature of digital halftones, the highlight and shadow areas will be most difficult to control. Secondly, use of a screen angle can limit the filling-in in the tone production curve. Thirdly, the variability of the spot size on paper, and its irregularities must be closely observed to assure that these dot forms will be reproducible in the lithographic process if this is desired. And finally, careful planning in the design of a halftone dot may allow an improved tone production curve.

Library of Congress Subject Headings

Nonimpact printing; Laser printing

Publication Date

1-1-1988

Document Type

Thesis

Department, Program, or Center

School of Print Media (CIAS)

Advisor

Cost, Frank

Comments

Note: imported from RIT’s Digital Media Library running on DSpace to RIT Scholar Works. Physical copy available through RIT's The Wallace Library at: Z252.5.N64 H354 1988

Campus

RIT – Main Campus

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