Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!mips!spool.mu.edu!cs.umn.edu!thelake!steve From: steve@thelake.mn.org (Steve Yelvington) Newsgroups: comp.text.desktop Subject: Re: Re: DTP books Message-ID: Date: 22 Apr 91 16:11:26 GMT References: <1991Apr20.163349.14280@gdt.bath.ac.uk> Organization: St. Croix Valley C and Ski Lines: 57 [In article <1991Apr20.163349.14280@gdt.bath.ac.uk>, ma9mgg@gdt.bath.ac.uk (M G Gidley) writes ... ] > Also, does anyone know a decent book about printing methods (ie the different > process - litho etc, screening photos). I have the constant problems of > contacting printers and them blinding me with jargon so I'd like to find > out more rather than claim ignorance ! I'm not sure what books might be available in the U.K., but here are some definitions that you might find helpful. Feel free to ask for more; it's a far more appropriate use of the net than the flame wars you see in most newsgroups. Lithography: Literally, ``stone printing.'' Traditional lithography (still used by many artists) employs a stone surface onto which an image is drawn using a greasy crayon. The stone surface then is dampened. The moisture won't stick to the greasy image, but it coats the stone. An ink roller then is applied to the moistened stone. The oily ink won't adhere to the damp areas, but sticks nicely to the image area. You then press a piece of paper over the stone, and the image is transferred to the paper. Modern commercial lithography uses a flexible aluminum plate in place of the stone, and a photosensitive coating in place of the greasy crayon. The coating is exposed to light through a photographic negative. Unexposed areas then are removed in a developing process. The resulting plate then is mounted on a rotary press. Offset: Actually, ``offset lithography.'' Instead of letting the paper come into direct contact with the printing plate, the image is ``offset'' first onto a rubber roller or ``blanket'' and then transferred to the paper. By avoiding direct contact between the rough surface of the paper and the printing plate, abrasion is reduced. Also, since the rubber is slightly flexible, it can deposit the ink onto the paper more evenly. Most modern lithography is offset. Letterpress: The traditional Gutenberg method of printing whereby a raised surface is inked and pressed into the paper. Letterpress printing from phototype (or laser type) requires that an engraving be made. Gravure: This is sort of a mirror image of letterpress. The inked areas actually are engraved into a smooth surface, usually copper. Ink flows onto the surface, then is scraped off (except in the depressed channels). The paper then is placed into contact with the plate. Gravure (called rotogravure if it's a rotary press) is quite expensive, but yields high quality over extended press runs. Screening photos: By nature, photographs are ``continuous tone'' images (at least at a macro level). They're a mixture of grays. Since printing deals with only binary states -- there's either ink there, or there isn't -- the grays have to be simulated by breaking the image into dots whose sizes are in proportion to the density of the original image. A screened photo is often referred to as a ``halftone.'' Traditionally, halftones have been created using photo-optical techniques, but now you can produce them digitally by scanning the image into a computer and using appropriate software. ---- Steve Yelvington, Marine on St. Croix, Minnesota, USA / steve@thelake.mn.org