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A PARTIAL DOT ALGORITHM FOR MULTI-LEVEL PIXEL HALFTONE CELLS

IP.com Disclosure Number: IPCOM000025991D
Original Publication Date: 1989-Aug-31
Included in the Prior Art Database: 2004-Apr-05
Document File: 2 page(s) / 116K

Publishing Venue

Xerox Disclosure Journal

Abstract

Partial dotting is a method whereby images recorded as 8 bits, or 256 levels, per pixel are converted to a halftone screen representation suitable for rinting on devices where the reflectance of a pixel is limited to. a few distinct revels. Conventional methods have dealt only with binary pixel printing. The algorithm to be described expands this capability to an arbitrary number of bits per pixel.

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XEROX DISCLOSURE JOURNAL

A PARTIAL DOT ALGORITHM FOR MULTI-LEVEL PIXEL HALFTONE U.S. C1.346/140R CELLS Int. C1. Gold 15/16 Thomas Henderson
John F. Knapp

Proposed Classification

Halftone procedure:

18 Bit Pile1 Input

I

12 Bit Pixel Output 1

0000000000000000

0000001000000000

0000011000000000

Line 2 Pixel 2 3333333333333333

3333333333333332

4 Pixel Counter:

 Mod 4. 4 + Mod 4, 8 + Mod 4,
. 12+Mod4

1)

FIG. I

Partial dotting is a method whereby images recorded as 8 bits, or 256 levels, per pixel are converted to a halftone screen representation suitable for rinting on devices where the reflectance of a pixel is limited to. a few distinct revels. Conventional methods have dealt only with binary pixel printing. The algorithm to be described expands this capability to an arbitrary number of bits per pixel.

Volume 14 Number 4 July/August 1989 175

[This page contains 1 picture or other non-text object]

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A PARTIAL DOT ALGORITHM FOR MULTI-LEVEL PIXEL HALFTONE CELLS (Cont'd)

In binary printing one must decide between only two alternatives when printing a pixel, whether it is black or white. For pictorial reproduction the decision between black or white has been made by comparing an originally recorded 8 bit pixel value against one element of an array of threshold values. If the 8 bit value exceeds that threshold, the pixel is printed black and otherwise remains white. In this way the halftone dot is grown from 0 to 100 percent coverage. All the information about the halftone screen is contained in the threshold matrix and a shift parameter that enables screen angles. This state of affairs is complicated considerably when one can print multi-level pixels. Now the threshold algorithm will not work because it yields only a two state outcome while the pixel to be printed has more than two states. This proposal provides a new partial dot algorithm to solve this problem.

The heart of this new a1 orithm is a look up table. The basic element in thi...