PrintingHalftones.ppt

Printing Origin of Printing Invented by Chinese c.1000 AD Entire page printed at once wood cuts metal type Reinvented in Europe, Johannes Gutenburg Entire page printed at once movable type, could ‘reset’ the plate Traditional Printing Processes Intaglio Letter press / Relief Silk screen / Porous / Stencil process Lithography / Planographic Lithography/Planographic Process Image and non-image areas are on the same plane. Difference: Receptivity of ink Image areas accept ink Non-image areas repel ink The plate image is the same as the print. Intaglio Printing The image is etched or depressed into the plate as small wells, which contain ink. Non-image areas are the surface of the plate. The plate image is the reverse of the final print. Letter/Relief Press The image area is raised and inked. The non-image area is depressed. The plate image is the reverse of the final print. Silk Screen/Porous/Stencil Process Image areas are porous allowing ink to pass through. Non-image areas are non porous. Metal, nylon, silk screen, or fibrous material is used. The plate image is the same as the print. Binary Printing The traditional printing processes described maintain only two tones: Binary Printing How do printers produces gray tones between the traditional ink and no-ink areas without many gray inks? The Halftone Idea Make a grayscale … with discrete levels of gray. The Halftone Idea Early artists used the Halftone Idea and alternatives to make gray with dots or lines: Stippling, lithography, mezzotint, etc. The Halftone Idea Levels of Gray Decrease the amount of black concentrated in an area to make it look lighter: spaced lines and dots Increase the area covered in black to darken it: condensed lines and dots The Halftone Idea The spacing and size of markings used to simulate gray depend on: Human Visual System: Don’t want people to distinguish lines / spots Roughly, people see up to 60 lines per inch (lpi) at 2 ft. Viewing Distance The Halftone Idea Two Types