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Image Halftoning Disclosure Number: IPCOM000061987D
Original Publication Date: 1986-Sep-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 1 page(s) / 12K

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Helms, RM: AUTHOR [+1]


This idea provides for an increase in number of gray shades when halftoning using a fixed pattern.

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Image Halftoning

This idea provides for an increase in number of gray shades when halftoning using a fixed pattern.

When halftoning a gray scale image to a bi-level image, a pattern of dots is used to simulate a level of gray by varying the number of black printing elements in comparison to the overall number of possible printing elements in a fixed pattern size. Normally, in a two by two pattern, one can obtain five shades of gray, namely all white, all black and three intermediate shades resulting from the selection of one, two and t elements.

Elements printed using wire matrix printers are typically larger than the area that is really needed, in order to yield smooth image edges. As a result, the selection of differing pairs of elements in a two by two pattern may result in differing area ratios of black to white. Printing two adjacent elements would produce less coverage than if two diagonal elements are printed. That is, more physical overlap of the dots occur from two adjacent elements. It has been verified through experimentation that seven shades of gray of the resulting dots can achieved with the selection of elements from a two by two array. The differing shades result from selecting zero elements and four elements at the extreme and, in between, vary from one element, two elements horizontally adjacent, two elements vertically adjacent, two diagonal elements, and three elements, resulting in the seven shades of gray. However, if the vertical resolution...