39. Half-tones
Picture from designer-info.com.
The half-tone process is used to reproduce any subject with continuous varying tones, such as photographs, shaded-in or wash drawings, air-brush work, and drawings in which the lines are so closely spaced that they would reproduce as tonal gradations.
Half-tone illustrations are generally more costly to reproduce than line drawing. Photographs may need retouching by expert hands, or the tonal contrasts may require heightening. Another consideration is the compatibility of the printed half-tone with the rest of the artwork, especially since it demands a certain quality of paper for satisfactory reproduction. We have all come across relatively expensive books which have half-tones like poor photocopies — mostly a sludge of black ink with a few dim details barely discernible. New tech doesn’t always serve the reader as well as it might.
Line drawing may sometimes be more appropriate, and less expensive, for the subject matter and presentation required. In order to produce a continuously toned subject, a printer overlays the photographically sensitive material with a screened (grid-like) glass plate or negative, which has the effect of breaking up the image into a pattern of dots. Dark areas of the original are reproduced by large dots with less separation than the smaller points representing lighter areas. In this way, tone and shape are built up on the plate. Newspaper pictures are traditionally printed this way.
You must always be careful not to submit a printed screened picture for printing — and hence further screening — without making sure that the printer adjusts the screen adequately to eliminate that irritating wavy effect you can sometimes spot in cheaply produced brochures.
Next: 40. Validating Technical Illustrations.
August 2nd, 2006 at 5:05 pm
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