Browse Prior Art Database

Halftone Image Produced by Pseudo Random Bit Generator

IP.com Disclosure Number: IPCOM000082406D
Original Publication Date: 1974-Dec-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 2 page(s) / 33K

Publishing Venue

IBM

Related People

Smith, GL: AUTHOR

Abstract

This halftone image generator is for use in driving an on/off printer to reproduce the halftone image of an original.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 61% of the total text.

Page 1 of 2

Halftone Image Produced by Pseudo Random Bit Generator

This halftone image generator is for use in driving an on/off printer to reproduce the halftone image of an original.

The original continuous-tone image is scanned through a screen.

For each individual screen area, its gray tone level, or localized reflectance value, is defined by one of seventeen possible binary numbers defining seventeen gray levels. The binary level "0" defines a white area, whereas the binary level "16" defines a black area.

A pseudo-random bit generator 10 is driven by a constant-frequency clock at a frequency which is higher than the sampling frequency of the image screen areas. For example, the bit generator 10 cycles four times for each image screen area.

Each gray level binary signal, defining the gray level of a particular screen area, is applied as a partially enabling input to specific AND's 11-15. As assumed, this gray level signal is maintained for four cycles of the bit generator
10.

The AND's 11-14 which are partially enabled by the gray level signal are completely enabled, on a mutually exclusive basis, by the binary state of particular stages of the bit generator 10. Note that the binary state of the bit generator changes four times during a given gray level signal.

The interconnection of the AND's to the bit generator 10 is such as to provide a progressively higher probability of an AND output occurring, as the gray level increases toward "black" or a binary 16.

The AND's d...